Lisa Murkowski, Chuck Grassley.

Carl P. Leubsdorf, Tribune News Service

Last January, Donald Trump helped the Democrats regain control of the Senate in two crucial Georgia runoffs, raising questions about the state’s election procedures that prompted a falloff in the normal GOP voter turnout.

Less than three months later, there are signs the former president’s determination to maintain an active role in GOP politics may be complicating his party’s bid to regain the Senate in next year’s midterm elections.

Already, five incumbent Republican senators have decided to retire, all of whom would have been favoured for reelection and some who might have faced primary challenges from Trump supporters. With most incumbent Democrats seemingly safe reelection bets, the GOP can’t afford to lose these seats if it is to regain the majority it lost in January.

One persistent maxim of American politics is that the party that wins the White House loses congressional seats at the next midterm election. But recent history shows that far more consistently true for the House, which fills all 435 seats every two years, than for the Senate, where only one-third of 100 are contested.

In fact, in the last six elections occurring two years after election of a new president, the party in power twice gained Senate seats and twice lost only one. But it lost House seats in five of the six, mostly by double digits. Since senators serve six-year terms, the group facing the voters in any midterm election consists of those elected in a presidential election six years earlier. Those up in 2022 were elected in 2016, an unexpectedly good Republican year, and 2010, an excellent one.

As a result, 20 of the 34 Senate seats on the 2022 ballot are now held by Republicans and 14 by Democrats. At present, analysts see only three Democrats facing potentially serious challenges: Sens. Catherine Cortez Masto of Nevada, Maggie Hassan of New Hampshire and Raphael Warnock of Georgia, one of January’s unexpected victors.

Of the three, Warnock probably faces the most difficult reelection since Georgia remains closely divided politically. A recent New Hampshire poll showed Hassan trailing Gov. Chris Sununu, but it is unclear if the popular GOP governor will run.

Still, the biggest prizes next year may be the open GOP seats. While all 14 Democratic incumbents seem likely to run again, five of the 20 Republicans have already announced they won’t – Sens. Richard Shelby of Alabama, Roy Blunt of Missouri, Richard Burr of North Carolina, Bob Portman of Ohio and Pat Toomey of Pennsylvania. Three others – Sens. Chuck Grassley of Iowa, John Thune of South Dakota and Ron Johnson of Wisconsin – may join them.

Their prospects might increase if the GOP rejects the establishment Republicans who have traditionally done well there and nominates outspoken Trump supporters with potentially less appeal to more moderate general election constituencies.

Toomey and Burr are the only retiring GOP senators who voted to convict Trump in January’s impeachment trial. But several others angered the former president’s supporters. Blunt faced the prospect of a primary challenge from Eric Greitens, a pro-Trump Republican forced to resign as governor in 2018 amid a controversy over an extramarital affair. He entered the race last week, as did another stalwart Trump backer, state Attorney General Eric Schmitt.

The entire situation echoes 2010 and 2012, when more conservative GOP candidates lost general elections after beating establishment Republicans in Senate primaries. That helped the Democrats maintain their Senate majority for four years after they lost the House in 2010.

Trump has already made clear he will oppose his foes and help his supporters in 2022. He vowed to campaign against Sen. Lisa Murkowski, who also voted for conviction. A state official, Kelly Tshibaka, is challenging Murkowski with the support of key Trump 2020 operatives, but the independent Alaska senator has survived prior primary challenges.