Before November, several others among the “Biden 16” must beat back primary challenges from the conservative wing of the GOP.

In Nebraska, Bacon is facing perhaps his strongest primary test yet. If he wins, he will take on the same Democratic opponent, state Sen. Tony Vargas, whom he defeated two years ago by fewer than 3 percentage points.

Bacon has been a vocal supporter of sending more military aid to Ukraine, something opposed by his primary opponent, second-time congressional candidate Dan Frei.

Frei, who contends the GOP base is fed up with Bacon, accuses the incumbent of flouting campaign promises by voting to increase spending and for bills that do nothing to stem the flow of immigrants crossing the U.S.-Mexico border illegally.

Nearly all of the 16 races are considered toss-ups.

Republicans intend to hammer home a message about lax border security and high inflation under Biden. Democrats are warning that Republicans will pursue a national abortion ban as Democrats invoke an issue that has consistently worked in their favor at the ballot box since the U.S. Supreme Court overturned the constitutional right to an abortion in 2022.

North Carolina Rep. Richard Hudson, chair of the House Republicans’ campaign arm, said the “Biden 16” have formed strong identities in their districts and are emphasizing local issues.

Hudson said Biden’s unpopularity and presidential turnout models are increasingly giving an edge to Republicans, with the GOP attracting more working-class voters who more likely to vote in presidential elections and help flip these districts to Trump.

“The presidential turnout dynamics actually favor Republicans,” Hudson said in an interview. “And then if you look, state by state, where our battlegrounds are, the presidential turnout is going to help us.”

Washington Rep. Suzan DelBene, who leads the House Democrats’ campaign arm, said Democrats will highlight what they say is the chaos at the highest levels of government when Republicans are charge of the House and Trump is in the White House. They will say Trump is a threat to democracy and Republicans are extremists and hypocrites who voted against major spending bills under Biden and then tried to take credit for the projects that landed in their districts.

Voters “want folks who are there to govern,” DelBene said in an interview. “They’re not looking for extremism. And so all we have to do is make sure that voters are aware of what they’re doing. … Holding them accountable for their actual votes, even though their rhetoric sometimes tries to be more moderate.”

In Pennsylvania, Houck’s bid to unseat Fitzpatrick, who is backed by some labor unions and business groups, has a visceral feel that some Republicans say resonates with them.

At the Solebury Republicans’ meeting on the grounds of a luxury hotel and wedding venue, Houck unwound the story of his arrest, describing federal agents with guns drawn as they descended on his Bucks County home in 2022.

They arrested him, in connection with the incident outside a Planned Parenthood clinic in Philadelphia. Houck defended his actions, saying he acted to protect his 12-year-old son from abusive comments made by the clinic volunteer. The trial ended in an acquittal in 2023, and Houck, who runs a Catholic ministry group, said he began fielding requests to run for office.

Houck’s story struck a chord with Rose Cipriano, who came to hear him speak. Her husband picked up a Houck yard sign and Cipriano, who had previously supported Fitzpatrick, said Houck has changed her mind in the approaching primary.

“I’m looking for fresh ideas, and I’m willing to take a chance and vote for him on Tuesday,” Cipriano said “I’ve known his story since it happened, and I support him.”