EXCLUSIVE: WEST LEBANON, N.H. — When it comes to Sen. Bernie Sanders, former President Trump is no laughing matter.

The longtime independent senator from Vermont, progressive champion and two-time runner-up in the Democratic presidential primaries is on a two-day swing this weekend in neighboring New Hampshire as well as Maine to campaign on behalf of Vice President Kamala Harris to make sure the GOP presidential nominee doesn’t return to the White House.

“Trump cannot get elected. We’ve got to do everything we can to make sure that does not happen,” Sanders told a crowd of supporters during his first stop Friday in New Hampshire, a key swing state in presidential elections.

TRUMP MOVES TO DEFINE HARRIS AS ULTRA-LIBERAL

But minutes earlier, Sanders briefly broke out in laughter when asked in a national exclusive interview with Fox News about comments from Trump this week arguing that Harris — who has replaced President Biden at the top of the Democrats’ 2024 national ticket — is more liberal than the Vermont senator.

Trump over the past week has worked to define Harris, a former San Francisco district attorney and California attorney general, as an ultra-liberal, pointing to her record in the U.S. Senate and as vice president.

WHITMER CHARGES VANCE HAS ‘ABSOLUTELY BETRAYED’ HIS WORKING CLASS ROOTS

Speaking to a packed arena in Charlotte, North Carolina, on Wednesday, Trump charged that Harris was the “most incompetent and far-left vice president in American history… She is a radical left lunatic who will destroy our country if she ever gets the chance to get into office.” 

And mentioning Sanders, Trump argued that Harris is “more liberal than Bernie Sanders. Can you believe it?”

Former President Trump speaks at a campaign rally in Charlotte, North Carolina, on Wednesday. (AP Photo/Matt Kelley)

Sanders, responding, said, “I would hope that when he said, ‘Can you believe that?,’ people said no.”

“It’’s not true. Once again, Trump is lying,” Sanders emphasized. “Let me just simply say that for better or for worse, Kamala Harris is not more progressive than I am.”

During his Fox News interview and later at his event, Sanders took aim at Trump, who two months ago was convicted of 34 felony counts in the first criminal trial of a former or current president in the nation’s history.

“This is the most important election, I think, in our lifetimes. I will do everything that I can to see that Donald Trump is defeated,” the senator stressed.

REPUBLICANS ARGUE HARRIS REPLACING BIDEN AT TOP OF DEMOCRATS’ TICKET ‘UNDEMOCRATIC’

Sanders argued that “the American people will not and cannot accept a president who is a pathological liar, somebody who believes that women should not be able to control their own bodies, somebody who in the midst of massive heatwaves thinks climate change is a hoax and somebody who actually does not believe in democracy, has not said that he will accept those election results if he loses. So, for all of those reasons, Trump must be defeated.”

Sanders is campaigning on behalf of Harris, but he hasn’t formally endorsed the vice president.

Vice President Kamala Harris arrives for a campaign event in Milwaukee on Tuesday.  (Daniel Steinle/Bloomberg via Getty Images)

“I think if the vice president is to win this election, and obviously I want her to win, I think she has to start talking about issues of relevance to the working class of this country, because there are tens of millions of people who are really hurting,” Sanders explained. “They want to know what the next president is going to do for them, and I hope very much that Vice President Harris will make that clear.”

“The path towards victory is to talk about issues that are relevant,” he reiterated.

Asked what Harris specifically needs to detail, Sanders said, “I hope that the vice president will be talking about the need to substantially lower prescription drug costs… the need to have tax reform so the wealthiest in this country start paying their fair share of taxes, so we can greatly expand child care and affordable housing in this country, and I think we’ve got to be very strong on the issue of climate change and make it clear that we’re going to transform our energy system away from fossil fuel if we’re going to save this planet for future generations.”

Sanders said that Harris’ choice of a running mate — which is expected to come in the next two weeks — will be a signal of whether she will project a progressive agenda as she runs for the White House.

“I think it will, and I hope very much she looks at one of the many progressive people who are out there who I think would do a good job as vice president,” the senator said.

Sanders was making his swing through New Hampshire and Maine less than a week after President Biden suspended his 2024 re-election rematch with Trump. Biden made his move amid mounting pressure from within the Democratic Party for him to drop out after a disastrous performance in last month’s first presidential debate with Trump. 

Sen. Bernie Sanders of Vermont speaks to supporters at a campaign event on behalf of Vice President Kamala Harris in West Lebanon, New Hampshire on Friday. (Fox News – Paul Steinhauser)

The embattled president’s immediate backing of Harris ignited a surge of endorsements of Harris by Democratic governors, senators, House members and other party leaders. By Monday night, the vice president announced that she had locked up her party’s nomination by landing the backing of a majority of the nearly 4,000 delegates to next month’s Democratic National Convention. On Friday morning, former President Obama and former first lady Michelle Obama were among the final major party leaders to endorse the vice president.

Harris has also hauled in a staggering $129 million in fundraising since Biden’s announcement, her campaign touted on Thursday morning. 

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Republicans charge that the process has been anything but democratic — and they point to Biden’s own words.

Before dropping out, the president had repeatedly cited the 14 million votes he won in this year’s Democratic presidential primaries as a reason he should stay in the 2024 race.

“The voters — and the voters alone — decide the nominee of the Democratic Party,” he emphasized in a letter on July 8. “Not the press, not the pundits, not the big donors, not any selected group of individuals, no matter how well intentioned.”

Trump, at his rally in Charlotte on Wednesday, called the switch at the top of the Democrats’ national ticket “an undemocratic move.” 

“These are nasty people, the Democrats,” Trump argued.

And Republican Sen. Tom Cotton of Arkansas claimed in a social media post this week that “Joe Biden succumbed to a coup by Nancy Pelosi, Barack Obama, and Hollywood donors, ignoring millions of Democratic primary votes.”

But Sanders, who argued during his marathon 2016 Democratic presidential primary battle against eventual nominee Hillary Clinton that the party was working against him, doesn’t buy the GOP criticism.

“These are extraordinary times and the Democrats had to move very quickly,” Sanders said. “So I think that given the reality that Biden dropped out and having a Democratic convention coming, I think what happened is she announced her candidacy, she rallied the support she needs, and I think that’s fine.”

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.

BUTLER, Pa. – Whistleblowers have told Republican Missouri Sen. Josh Hawley that a law enforcement officer who was assigned to monitor the roof of a building that would-be former President Trump assassin Thomas Crooks fired from on July 13 left their post because it was “too hot.”

Crooks, 20, fired multiple rounds from the roof of American Glass Research (AGR) Building 6, which was outside the rally perimeter but had a direct line of sight to where the former president was standing on stage at his campaign rally in Butler, Pennsylvania.

“This comes from a whistleblower with direct knowledge of the Secret Service plan and setup that day,” Hawley said. “And what this whistleblower tells my office is that there was at least one law enforcement person assigned to the roof itself. In other words, the plan called for a law enforcement individual to be on the roof at all times during the rally. And that did not happen. And what the whistleblower tells me is the law enforcement individual who was assigned to that roof abandoned it.”

Butler’s temperature reached a high of 92 degrees on July 13, and prior to the assassination attempt, emergency personnel at the rally were mostly focused on attending to people suffering from heat-related illnesses.

TRUMP ASSASSINATION ATTEMPT AFTER SECRET SERVICE FAILURES PROMPTS CALLS FOR DRASTIC AGENT RECRUITMENT CHANGES

Hawley, who visited the rally site on Friday, noted that the AGR building in question was about 150 yards or fewer from the main stage of Trump’s rally.

TRUMP SHOOTING: TIMELINE OF ASSASSINATION ATTEMPT

While Congress has confirmed that Crooks purchased a ladder at Home Depot prior to the rally shooting that left 50-year-old firefighter and father Corey Comperatore dead and two others — 57-year-old David Dutch and 74-year-old James Copenhaver — critically wounded, he could have accessed the roof of the AGR building without a ladder. Lawmakers who visited the site on Monday were able to reach the roof without a ladder.

“…He or she was too hot and just thought it was unnecessary to be out there.”

— Sen. Josh Hawley, R-Mo.

The same whistleblower told Hawley that multiple law enforcement personnel were also assigned to patrol the perimeter of the building “to make sure that somebody couldn’t just jump up” onto the roof, possibly from one of the air-conditioning units jutting out from the windows of the building, the senator said.

The Butler Farm Show in Butler, Pennsylvania, site of a campaign rally for former President Trump, is seen on July 15. Trump was wounded on July 13 during an assassination attempt while speaking at the rally. (AP Photo/Gene J. Puskar)

The roofs at the Butler Fair Ground in Pennsylvania, where a group of bipartisan lawmakers visited on Monday. (Fox News Digital)

“All of these whistleblowers who’ve now come forward to my office, saying things like: law enforcement was assigned to be on the roof, and they weren’t. They were assigned to be patrolling the perimeter of that building, and they weren’t. They were supposed to be communicating over a common radio frequency, and they weren’t,” Hawley said. “I have to say, none of that surprises me because it is just astounding with those kind of failures and errors that this 20-year-old was able to get up on in plain view of everybody onto that low-slung roof and take multiple shots at the [former] president.”

AIR FORCE VETERAN AT TRUMP RALLY SAYS ‘SOMETHING WASN’T RIGHT’ BEFORE WOULD-BE ASSASSIN OPENED FIRE

Approximately one hour passed between the time law enforcement officials first identified a suspicious person near the rally grounds and the time Crooks fired. Officials temporarily lost sight of the suspicious person, but then around 5:52 p.m., a sniper “had eyes on him,” which was about 20 minutes before the gunfire rang out, Hawley said, citing a briefing he attended with former Secret Service Director Kimberly Cheatle last week.

The whistleblower also told Hawley that the Secret Service had delegated the AGR building and the roof to local or state law enforcement but noted that both local and federal officials have been pushing blame onto one another.

PENNSYLVANIA OFFICERS NOT ALLOWED IN SECRET SERVICE COMMAND CENTER AT TRUMP RALLY, LAWMAKERS SAY ON SITE

“There’s a lot of effort on the part of both Secret Service, on the one hand, and DHS on the other hand, and then also state and local law enforcement to push the responsibility off onto each other. So this is just why we need to get these facts into the open. We need to have real and substantive hearings, not like the one [on Monday] where the former Secret Service director wouldn’t even respond to questions. What a farce that was,” Hawley said.

Thomas Crooks seen at the Trump rally on July 13 in Butler, Pennsylvania. (Sen. Ron Johnson)

His comments came the same day Cheatle resigned from her position on Tuesday morning.

“To the Men and Women of the U.S. Secret Service, The Secret Service’s solemn mission is to protect our nation’s leaders and financial infrastructure,” Cheatle wrote in a letter to the agency obtained by Fox News. “On July 13th, we fell short on that mission.”

TRUMP SHOOTING SITE GIVES BIRDS-EYE VIEW OF ‘DISORGANIZED’ RALLY SCENE, WITNESSES SAY

Cheatle said that the “scrutiny” over the last week “has been intense and will continue to remain as our operational tempo increases.” 

WATCH: EYEWITNESS SHARES NEW FOOTAGE OF TRUMP SHOOTING

“As your Director, I take full responsibility for the security lapse,” she wrote.

Now, Hawley is calling for Department of Homeland Security (DHS) Secretary Alejandro Mayorkas to resign, as well.

Sen. Josh Hawley, R-Mo., left, is calling for Homeland Security Secretary Alejandro Mayorkas to resign in light of the assassination attempt against former President Trump. (Getty Images)

“Alejandro Mayorkas needs to resign. He’s the head of DHS. All of this is in his purview — Secret Service, the DHS personnel,” the Missouri senator said. “Another whistleblower tells me that most of the federal security there that day were not Secret Service. Most of them were DHS personnel who had just been detailed over to this event for the day. And they were largely not prepared, not read into the security plan, and were not executing their duties according to what the plan called for.”

TRUMP ASSASSINATION ATTEMPT: BUTLER, PENNSYLVANIA TOWN MANAGER DEFENDS POLICE AMID RESPONSE ‘MISCONCEPTION’

Hawley suggested the DHS is overwhelmed under Mayorkas’ leadership of the agency. 

A DHS spokesperson said the agency “cannot comment on matters related to an ongoing investigation. We, of course, are committed to working with the appropriate and relevant investigations of what happened on Saturday, including with Congress, the Inspector General, and both internal and independent reviews.”

The Secret Service did not respond to an inquiry from Fox News Digital regarding Hawley’s comments.

“The Department of Homeland Security is in total crisis.”

— Sen. Josh Hawley, R-Mo.

“I think the fact that you have so many of these DHS security folks, a lot of them are designated as investigators — DHS investigators — whose jobs are actually to be out in on the ground in the continental United States, searching for illegals, looking for crime. So many of them have been sent to the southern border. So there aren’t that many of them available to begin with. And then you’re pulling people off of other responsibilities and sending them to this rally. They’re not adequately briefed. They’re not trained to do that,” Hawley said. 

Mayorkas on Sunday announced that he has tapped a bipartisan panel of law enforcement experts to conduct a 45-day independent review of the assassination attempt.

“The men and women of the U.S. Secret Service make it the greatest protective service in the world, with one of the most solemn and difficult missions in government,” the DHS secretary said. “This independent review will make the organization even better.”

Hawley’s office continues to communicate with whistleblowers about the Trump rally shooting and what went wrong in order for Crooks to gain access to the AGR building rooftop that evening with an AR-15.