Sen. Mitt Romney’s exit from Congress in January leaves the already shrinking moderate bloc in Congress one man short. For the Republican conference, his seat is safe in Utah, a deeply red state. But it may not be occupied by a centrist like Romney.

He is one of the few Republicans in the Senate who voted to impeach former President Donald Trump. And Trump held that against Romney, jumping to call him “RINO,” or Republican In Name Only, a criticism leveled by conservatives against members of their party for being liberal.

At the time of the impeachment vote on Feb. 6, 2021, Romney acknowledged the consequences of his decision, should he follow his conscience, in his journal, as published in his latest biography.

“My colleagues in the Senate would have nothing to do with me. It would affect my ability to get any legislation passed. I’d get nothing done through the administration, of course,” he wrote. “For the rest of my life, I would be accosted by people who hate what I had done — if I just vote with party, my vote would be expected and people who dislike Trump would just dismiss me as a callous Republican, but voting against party would engender true enmity and vitriol.”

As Romney predicted, he did splinter away from many hardline conservatives, but the Utah senator found new friends as the pandemic began to unfold.

A group of senators — four Republicans and four Democrats — ate takeout for dinner at Alaska Sen. Lisa Murkowski’s home during COVID-19, Romney said at an event with former House Speaker Paul Ryan. They sat six feet apart and discussed policy.

The Republicans in the group included Sens. Romney, Murkowski, Susan Collins of Maine and Rob Portman of Ohio. The Democrats were Sens. Kyrsten Sinema, who has since registered as an independent, Joe Manchin of West Virginia, Jon Tester of Montana and Jeanne Shaheen of New Hampshire, as the Deseret News reported.

This group was influential in the passage of several bipartisan bills like a COVID-19 stimulus bill under Trump, as well as the infrastructure bill, the CHIPS Act and the Respect for Marriage Act under Biden.

In September 2023, Romney said he won’t run for reelection and will finish serving in office in January 2025. At the time, he said, “I’m hoping that in the year and a half I have left that we’re going to be able to take on some of those issues, particularly as it relates to the deficit and debt and immigration,” he said.

His retirement coincides with many other moderate senators bowing out of running for reelection or facing an uphill battle to victory. The middle lane in Congress has been shrinking for decades, political science professor Michael Lyons at Utah State University told the Deseret News.

“Moderates often struggle to win party nominations because primary election turnout is low, with motivated, highly ideological voters becoming dominant by default,” he said. “Additionally, population movement has made many states far more homogeneous ideologically.”

He said only five states have “split” Senate delegations but “From 1973 to 1994, there were never fewer than 20 such delegations.”

Collins is up for reelection in 2027, while Murkowski’s and Shaheen’s terms in Senate end in 2029. Here’s what others from their caucus are up to.

Sen. Joe Manchin

Following Romney’s retirement news, Manchin of West Virginia, too, announced he isn’t running for reelection. His term also ends in 2025. At the time of his announcement, Romney said on X, formerly known as Twitter, he will miss the “American patriot in the Senate,” but noted that their friendship and commitment to American values will continue. Manchin has regularly worked with Romney. The two worked together on legislation like the infrastructure bill and pandemic-era relief.

Rumor has it Manchin is mulling a last-minute presidential bid for 2024. A political action committee is also working to recruit Romney and Manchin for a unity third-party presidential ticket.

Former Sen. Rob Portman

Rob Portman left office on Jan. 3, 2023, after deciding to not seek another six-year term in the Senate two years prior. He had two reasons for stepping down: He wanted to spend more time with his family and he was sick of the partisan gridlock in Washington, D.C. “It’s getting harder and harder to get things done,” he told reporters in 2021.

Portman’s seat is now held by the Trump-backed Sen. J.D. Vance, whom Portman endorsed in 2022. This endorsement came even though the two candidates had starkly different positions. Vance opposed the bipartisan infrastructure bill, which Portman helped negotiate, calling it a “hatchet job” in 2021. He has also consistently stood against funding Ukraine, while Portman served as the co-chair of the Senate Caucus on Ukraine during his tenure.

Sen. Kyrsten Sinema

The independent senator hasn’t officially decided whether she plans to run for reelection in 2024. Candidates Kari Lake and Pinal County Sheriff Mark Lamb are running for the Republican nomination, while Rep. Ruben Gallego is seeking the Democratic nomination, in addition to several lesser-known candidates, as the Deseret News previously reported. Should Sinema run, she is banking on support from at least 24% of registered Republicans, only about 10% to 20% of Democrats, and 60% to 70% of independent voters, according to a leaked campaign memo from September.

Right now, Sinema is heavily involved in efforts to secure bipartisan border security funding. She told The Wall Street Journal the negotiations are “definitely the hardest thing we’ve done,” adding that the crisis at the southern border can no longer be ignored.

Sen. Jon Tester

The Democratic Montana senator remains popular in the red state where Trump won in 2020. But popularity doesn’t guarantee a successful reelection. As The Associated Press reported, Tester has narrowly won the last three elections. But the Republican conference is expected to spend millions backing GOP candidates in hopes of gaining control of the Senate. Cook Political Report previously said the race will “lean Democratic” but now it’s a “toss-up.”

Aerospace founder and CEO Tim Sheehy is a Republican candidate running against Tester. He has garnered endorsements from Sens. Steve Daines of Montana, Tom Cotton of Arkansas and Marsha Blackburn of Tennessee, as well as Senate Minority Whip John Thune of South Dakota. Former Montana Secretary of State Brad Johnson is also in the running.