Republican senators are gearing up for the possibility of primary challenges ahead of the 2026 midterms as they seek to navigate the new political environment of a second Trump administration.
Taking out a sitting senator in a primary would be no easy task, but some in the right flank of the party have flirted with challenging incumbents who voted to convict President-elect Trump in his impeachment trial in 2021 or have more recently expressed reservations about his Cabinet picks.
Here are five Republican senators who could face primary challenges ahead of 2026.
Joni Ernst
Sen. Joni Ernst (R-Iowa) is facing criticism from a number of Trump allies for raising doubts about Pete Hegseth, Trump’s pick to lead the Pentagon.
The senator is seen as a key swing vote on Hegseth. She is the first female combat veteran to serve in the Senate and has been a vocal advocate for addressing sexual misconduct in the military. Hegseth, on the other hand, has faced sexual misconduct allegations, which he denies, and has said in the past he would like to block women from serving in combat roles in the military.
Iowa conservative media personality Steve Deace suggested this week on the social platform X that he would be willing to run against Ernst in 2026. Meanwhile, Iowa Attorney General Brenna Bird criticized “D.C. politicians” in a Breitbart op-ed earlier this week in which she called on the Senate to confirm Trump’s Cabinet nominees. Bird’s spokesperson said the article, which was widely seen as a warning shot, was about the entire Senate.
The comments followed Ernst’s initial cool public feedback to Hegseth. She has since seemed to change tune, offering support to the Pentagon nominee.
On Friday, Hegseth told Fox News that Republican senators should not be primaried if they vote against him.
Other Republican senators have also come out in support of Ernst during the process.
“The approach is going to be, ‘Everybody toe the line. Everybody line up. We got you here, and if you want to survive, you better be good. Don’t get on Santa’s naughty list here, because we will primary you,’” Alaska Sen. Lisa Murkowski (R) said during a recent discussion hosted by the centrist group No Labels.
“My friend Joni Ernst, who is probably one of the more conservative, principled Republican leaders in the Senate right now, is being hung out to dry for not being good enough.”
Ernst also has received praise from her GOP allies for her work as the founder and chair of the Senate DOGE Caucus, which is a nod to Trump’s “Department of Government Efficiency.
Thom Tillis
Sen. Thom Tillis (R-N.C.) kicked off his reelection campaign this week, and he’s on track to be one of the most vulnerable Senate incumbents this cycle.
He’s seen as another one of the potential Republican obstacles to Trump’s Cabinet nominees after expressing skepticism about former Rep. Matt Gaetz (R-Fla.), Trump’s now-withdrawn attorney general pick, and Pete Hegseth, his choice for Defense.
And although Tillis has said he’s not worried about a primary challenge if he votes down one or more of Trump’s top-level picks, he acknowledged there’s a sort of pressure campaign over the nominees.
North Carolina is set to be one of the most competitive states in the fight for the Senate in 2026 — and upset from the right could make Tillis even more vulnerable.
“It’s more important to get behind closed doors, address concerns and have Republicans come together as one, than to create controversy. I just think … it’s a short-term win, but a long-term loss, if you’re not careful with that,” Tillis told reporters, per footage from MSNBC.
A poll released this month from the Florida-based firm Victory Insights found that Lara Trump — the president-elect’s daughter-in-law and a North Carolina native who just stepped down from her role as co-chair of the Republican National Committee — would “likely crush” Tillis in a hypothetical GOP primary.
Lara Trump, though, hasn’t expressed public interest in running for the role, and it’s speculated she could be chosen to fill a possible U.S. Senate vacancy in Florida if Sen. Marco Rubio (R-Fla.), Trump’s pick for secretary of State, gets confirmed.
But the poll is a potential signal that the right primary challenger could pose a big problem for Tillis as he looks to win his third term in the upper chamber.
Tillis defeated his 2020 Democratic rival by just 2 points, and Democrats have long been searching for inroads in the key battleground, which they’ve lost by narrow margins across the past four cycles.
Susan Collins
Sen. Susan Collins (R-Maine) has said she plans to run for her sixth term as the rare Republican senator of a largely blue state, a move that would make her the longest-serving senator in Maine history and could scramble Democrats’ chances of winning back the upper chamber.
Democrats have long looked at Collins’s seat as a flip opportunity, but the centrist has scored decisive reelection wins against rivals across the aisle.
She’s been willing to buck her party in the past — like when she joined six other Republicans in voting to convict Trump on impeachment charges related to Jan. 6. That’s helped her appeal to independent and Democratic voters in her state, but it’s upset others in the GOP.
Collins voiced reservations about Trump’s nomination of Gaetz to lead the Justice Department, and said she found some of Robert F. Kennedy Jr.’s past statements “alarming” as he looks to lead the Department of Health and Human Services (HHS).
So although Collins running for reelection would give the GOP a boost in their efforts to keep up their Senate numbers, there’s the question of whether she’s irked her side enough to face a serious primary challenge.
And a GOP challenger could spell trouble for Collins. Since winning her seat, she’s never faced a primary challenger — and despite her 2014 reelection victory of nearly 40 points, she notched another term by a comparatively narrow 9 points in 2020 against former state House Speaker Sara Gideon (D), as Democrats were energized by Collins’s vote to confirm Supreme Court Justice Brett Kavanaugh.
But she’s shrugged off the pressure around Trump’s nominees.
“For me it’s an everyday occurrence, I mean that,” Collins recently told the Washington Post. “I get hit by the far left, in particular, and occasionally by the far right, all the time. So I’m used to that, that pressure.”
Bill Cassidy
Sen. Bill Cassidy (R-La.) is one of just three Republicans left in the upper chamber next year who voted to convict Trump on the impeachment charge of inciting insurrection, and that move could haunt him in 2026.
It’s already drawn him a primary challenger. Louisiana Treasurer John Fleming jumped in the race earlier this month, taking issue with Cassidy’s 2021 vote to convict as well as his support for Biden’s bipartisan gun safety bill and the bipartisan infrastructure bill. Fleming argued Cassidy has “failed the people of Louisiana” and that the state needs “a true conservative voice” in the seat.
Cassidy has yet to officially announce, but he’s signaled he’s preparing for 2026. And Fleming’s early announcement is a sign Republicans are ready and willing to challenge the two-term incumbent.
However, Cassidy is a formidable incumbent. The senator’s reelection campaign announced it raised $1.5 million in the third quarter of the year, closing out the quarter with $5.8 million in the bank. Additionally, Cassidy gave more than $2.2 million to Republican Senate candidates this past cycle.
And despite his conviction vote against Trump four years ago, Cassidy supported the now president-elect during his campaign this year. Cassidy said in a post on X in October he and Trump “will work together for the benefit of our state and our nation.”
Cassidy, a doctor and incoming chair of the Health, Education, Labor and Pensions Committee, has rejected claims attempting to like vaccines and autism, which HHS pick Kennedy has shared in the past — but has said he’s looking forward “to learning more” about Kennedy’s “other policy positions.”
John Cornyn
Sen. John Cornyn (R-Texas) plans to try for his fifth term in the Senate, but he could face a formidable primary challenge from other Texas Republicans — while Democrats grow more ambitious about flipping a Senate seat in the red state.
Speculation has swirled since the beginning of this year that Texas Attorney General Ken Paxton (R) could mount a bid for Cornyn’s seat, which could make for a contentious primary battle between the state’s MAGA wing and old guard.
During his unsuccessful bid to become the next Senate majority leader, Cornyn promised to get Trump’s nominees through the chamber quickly — but, though fear of a primary challenge could still give him pause about criticizing Trump’s picks, his leadership loss could give him more latitude to push back.
Paxton, meanwhile, has been embroiled in legal controversies, having been indicted on state securities fraud charges in 2015. Paxton won reelection by nearly 10 points in 2022, but he was also impeached and suspended from his post in 2023 by the GOP-controlled state House. The Texas Senate later voted to acquit him.
Meanwhile, Democrats are likely to be eyeing the seat after seeing inroads in red Texas in recent cycles. Rep. Colin Allred (D-Texas) built notable momentum in his bid to unseat Sen. Ted Cruz (R-Texas) this November, though he ultimately fell short by roughly 8 points.
But Cornyn has a history of fending off Republican primary and Democratic challengers. In 2014, the senator defeated then-Rep. Steve Stockman (R-Texas) by 40 points. Additionally, Cornyn defeated his Democratic challenger MJ Hegar in 2020 by nearly 10 points. Cornyn had Trump’s endorsement.
Of possible primary threats, Cornyn told Semafor last month that “if you’re afraid of elections, you’re in the wrong line of business.”
