(The Center Square) – Montana has one of the longest shares of the U.S. border with Canada of any state. However, it’s the other border – nearly 1,000 miles away – that is becoming a flashpoint in the state’s ongoing U.S. Senate race.

Montana’s U.S. Senate seat currently held by Democratic Sen. Jon Tester is up for re-election this year, with Tester running against Republican nominee Tim Sheehy, a former Navy SEAL and aerial firefighter. Sheehy has consistently attacked Tester on immigration and border security – seeking to paint him as an enabler of President Joe Biden’s record on illegal immigration from Mexico – forcing Tester to defend his record.

“What’s happening at the southern border is an absolute crisis, and it gets worse each day under the Biden administration and with career politicians like Jon Tester who talk a tough game about border security but aren’t getting the job done,” Sheehy writes on his campaign website. “The result of an open southern border is more crime and drugs flooding into our country and into our Montana communities.”

Since the Biden administration took office, over 7.9 million foreign nationals have illegally crossed the U.S. border with Mexico, according to U.S. Customs and Border Protection data, a figure that only includes those apprehended by law enforcement and not those who successfully sneak in between ports of entry. Many of these foreign nationals can remain in the country after submitting applications for asylum, which can take years to process.

“Jon Tester has worked hand in glove with Joe Biden to aid the invasion taking place at our southern border,” Sheehy wrote in a news release attacking Tester for voting to dismiss impeachment charges against Biden’s Homeland Security Secretary Alejandro Mayorkas. Sheehy has promised to support the construction of a physical wall along the southern border – a longtime policy goal of former President Donald Trump, the presumptive Republican presidential nominee – as well as end federal authorities’ relocation flights to distribute migrants around the country.

Sheehy’s focus on the border reflects a larger strategy for Republican Senate candidates in battleground states across the country, who have emphasized the issue. In April, a campaign arm of the Senate Republican Conference announced it would spend $15 million attacking Tester on immigration this election, according to Politico.

Tester, for his part, has played up the contrast between himself and Biden on this issue.

“I’ve stood up to Biden by demanding action to secure our border and protect Montana’s way of life,” Tester wrote on Twitter, now known as X, on June 9. Tester has also touted his support of a bipartisan border security bill introduced in the Senate in February and, again, in May, which Republicans voted against.

“We had one of the toughest border bills on the Senate floor we’ve ever had and Republicans killed it because they wanted to give my opponent a campaign issue,” Tester tweeted. Addressing his opponent directly, he wrote: “Tim – you didn’t even read the damn bill before you said you opposed it!”

Critics of the Senate bill Tester supports, however, said it would expand and codify the discretionary authority of Biden Homeland Security Secretary Alejandro Mayorkas when it comes to border-related issues. Using such discretionary authority, Mayorkas unilaterally changed laws established by Congress, including creating over a dozen parole programs, which House Republicans said are illegal and cited when they impeached him in February.

This year, Tester joined Republicans in Congress to support conservative immigration legislation – an unusual move for a Senate Democrat. Chief among these is the Laken Riley Act, a bill named for a Georgia graduate student allegedly killed by a foreign national in the country illegally, which passed the House in March and which Tester co-sponsored in the Senate.

Montana is regarded as a heavily conservative state with a Cook Partisan Voting Index (PVI) score of R+11, indicating a Republican lean. However, Tester has won re-election three times to his seat as a Democrat, and is currently the only Democrat holding a state-wide office.

Immigration is a major issue across federal campaigns this year as Democrats seek to blunt the Republican accusation that they are deliberately permitting illegal immigration, with Biden signing an executive order on June 4 that bans those who illegally cross the border from receiving asylum. However, he also issued an order on June 18 that would enable certain illegal immigrants who married U.S. citizens to obtain legal status and, eventually, U.S. citizenship themselves – which Republicans have derided as “amnesty.”

Not to be outdone, Trump last week announced that he would grant permanent residency to any international student graduating from a U.S. college or university. With over 1 million international students presently in the country, according to the Department of State, Trump’s proposal would represent the biggest expansion of legal immigration since the Reagan Administration, when a comprehensive immigration reform bill was last passed by Congress.

Tester and Sheehy did not immediately respond to requests for comment about whether they support Biden’s and Trump’s latest actions, respectively.