President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE is the leader of the Republican Party and has announced plans to run for reelection in 2020.

Yet for some Republicans, the question of whether to endorse him isn’t the easiest to answer.

“Why did you ask me that?” quipped Sen. Pat Roberts Charles (Pat) Patrick RobertsThe Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump seeks to flip 'Rage' narrative; Dems block COVID-19 bill GOP senators say coronavirus deal dead until after election MORE (R-Kan.), who announced his retirement this month.

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“Yeah, sure,” he said about endorsing Trump, before quickly emphasizing he’s more focused on policy work. “At this point I have some things I’d like to get done,” he said.

Sen. Susan Collins Susan Margaret CollinsGraham: GOP will confirm Trump's Supreme Court nominee before the election Gardner signals support for taking up Supreme Court nominee this year Tumultuous court battle upends fight for Senate MORE (R-Maine), who could face a tough race in a state that Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE carried in 2016, declined to comment on Trump’s reelection bid.

“I said I was going to worry about 2020 in 2020,” Collins said.

Sen. Ron Johnson Ronald (Ron) Harold JohnsonThis week: Supreme Court fight over Ginsburg's seat upends Congress's agenda GOP set to release controversial Biden report Democrats fear Russia interference could spoil bid to retake Senate MORE (R-Wis.), who could have a competitive race in 2022, says he is focused on rebuilding the state Republican Party in Wisconsin, which got crushed in the midterm election.

“That’s still a light year away,” he said of 2020. “What I’m doing, because I’m kind of the last man standing in Wisconsin, it’s about how do we continue to build our party and really develop a really good grass-roots effort. We got wiped out statewide last time so that’s where I’m focusing my attention.”

Sen. Ben Sasse Benjamin (Ben) Eric SasseChamber of Commerce endorses McSally for reelection Ben Sasse is mistaken with idea for the election of senators in America Big Ten football to return in October MORE (R-Neb.), who has frequently criticized Trump on foreign policy and trade issues, said, “I don’t talk about stuff like that right here” when asked outside the Senate chamber about whether he would endorse Trump.

Tensions between Trump and his party have ebbed and flowed over the years but are on the rise again after the longest government shutdown in history — which some Senate Republicans saw as a self-inflicted disaster for their party, driven by Trump.

The Senate passed a measure by voice vote in December that would have prevented the shutdown, only to see Trump reverse course from his communicated support for the bill.

A number of Republicans have also expressed growing frustrations with Trump’s foreign policy moves. On Thursday, 43 Republicans voted to end debate on an amendment warning Trump against drawing down troops in Syria and Afghanistan.

Trump remains the leader of his party and is a power in primaries.

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During one stretch this past summer, Trump went 11 for 11 in endorsing GOP candidates who went on to win their primaries, according to a tally by The Washington Post. The president sent out a scorching tweet against Rep. Mark Sanford Mark SanfordOn The Money: Business world braces for blue sweep | Federal Reserve chief to outline plans for inflation, economy | Meadows 'not optimistic' about stalemate on coronavirus deal Trump critic Sanford forms anti-debt advocacy group Republicans officially renominate Trump for president MORE (R-S.C.) on his primary day and watched as Sanford’s opponent, Katie Arrington, defeated the longtime politician and former governor.

Yet Arrington lost her general election contest in November, underscoring that while Trump is a power in primaries, he also has a toxicity that is costing his party some elections.

Maryland Gov. Larry Hogan (R) and former Ohio Gov. John Kasich (R) are making noises about challenging Trump in 2020. Neither seems too likely to defeat Trump and Republican office holders are hardly rushing to back them.

Sen. Cory Gardner Cory Scott GardnerGraham: GOP will confirm Trump's Supreme Court nominee before the election Gardner signals support for taking up Supreme Court nominee this year Tumultuous court battle upends fight for Senate MORE (Colo.), one of two Senate GOP incumbents running for reelection in a state won by Democrat Hillary Clinton in 2016, publicly endorsed Trump this week, telling the Independent Journal Review that he was throwing his support behind Trump because “we’ve done some good things for Colorado.”

Two other Republicans who will be Democratic targets next year were also enthusiastic about Trump.

“Absolutely. Look at the jobs report. Look at the economy. I think he’s done a wonderful job so, yes, certainly I would,” Sen. Joni Ernst Joni Kay ErnstGraham: GOP will confirm Trump's Supreme Court nominee before the election Joe Biden looks to expand election battleground into Trump country Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee MORE (Iowa) said when asked about endorsing Trump.

Sen. Thom Tillis Thomas (Thom) Roland TillisGrassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee Trump to include North Carolina in offshore drilling moratorium, senator says Biden's six best bets in 2016 Trump states MORE (N.C.), another potentially vulnerable Republican, acknowledged he had “a few instances where I disagreed with his style” but noted “on policy, for the most part, we’re in alignment.”

“I would discourage anybody from running against him in a primary,” he said. “If you take a look at his policies on tax reform, if you take a look at his priorities on trying to get health care to a place where it will work …. On substance I’m with him.”

Sen. David Perdue (R-Ga.), a fourth Republican up for reelection next year, said he would “absolutely” endorse Trump.

“With these results? Yes sir. This is the best economic turnaround in U.S. history,” he said.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellGraham: GOP will confirm Trump's Supreme Court nominee before the election Trump puts Supreme Court fight at center of Ohio rally The Memo: Dems face balancing act on SCOTUS fight MORE (R-Ky.), who is up for reelection and faced a primary challenge in his 2014 race, also set an example for his colleagues by announcing his support for Trump early out of the gate.

“I think he can go to the American people in 2020 and correctly claim extraordinary success," McConnell told The Washington Examiner in October.

But Trump appears to have more work to do to win over members of his party who have criticized his conduct or broken with him on major policy questions.

Sen. Mitt Romney Willard (Mitt) Mitt RomneyGraham: GOP will confirm Trump's Supreme Court nominee before the election Gardner signals support for taking up Supreme Court nominee this year Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee MORE (R-Utah), who famously warned his party against nominating Trump in March of 2016, told CNN’s Jake Tapper earlier this month that he hadn’t yet decided who he would endorse in 2020, although he ruled out mounting a primary challenge himself.

“I’m going to see what the alternatives are,” he said.

Sen. Lisa Murkowski Lisa Ann MurkowskiGraham: GOP will confirm Trump's Supreme Court nominee before the election Gardner signals support for taking up Supreme Court nominee this year Tumultuous court battle upends fight for Senate MORE (R-Alaska), who voted against Brett Kavanaugh Brett Michael KavanaughGraham: GOP will confirm Trump's Supreme Court nominee before the election Tumultuous court battle upends fight for Senate Fox's Napolitano: Supreme Court confirmation hearings will be 'World War III of political battles' MORE, Trump’s controversial nominee to the Supreme Court, declined to comment.

Sen. Tim Scott Timothy (Tim) Eugene ScottAuthor Ryan Girdusky: RNC worked best when highlighting 'regular people' as opposed to 'standard Republicans' Now is the time to renew our focus on students and their futures GOP lobbyists pleasantly surprised by Republican convention MORE (R-S.C.), who had misgivings in 2017 over how Trump responded to violence at a Unite the Right rally in Charlottesville, Va., predicted that Trump won’t need his endorsement.

“He’s not going to have a primary so there won’t be a decision to make,” he said.

But just because Senate Republicans aren’t ready to endorse Trump today doesn’t mean they won’t do so at a future date or that they are necessarily harboring qualms about his leadership.

Sen. Mike Rounds Marion (Mike) Michael RoundsChamber of Commerce endorses McSally for reelection Senate GOP eyes early exit Senate Republicans signal openness to working with Biden MORE (R-S.D.) said Trump is very popular in his home state but believes “it’s way too early” to be discussing an endorsement.

“I just haven’t gotten to the point I’m endorsing at this stage of the game.”