Ebullient Republicans returned to Capitol Hill on Tuesday after elections that put them on the brink of taking control of both chambers of Congress to face critical questions about how they will wield their power — and how tight a grip President-elect Donald Trump will have on their new majority.

GOP senators were set to make a monumental choice Wednesday, when, for the first time since 2007, they plan to elect a party leader not named Mitch McConnell. Three men have been quietly jockeying for months to replace McConnell, the longest-serving Senate party leader in history, but some of Trump’s allies have pressed him to block the man considered to be the front-runner: Sen. John Thune of South Dakota.

At the same time, Trump’s push to stack his administration with loyal members of Congress was colliding with a tough political reality for Republicans: They are running out of the bodies they need to preserve the narrow House majority they expect to hold.

With the party on track to win the House by a precariously small margin and Trump tapping two House members to serve in top national security posts, Republican leaders warned Tuesday that they could not spare any more.

“I don’t expect that we will have more members leaving, but I’ll leave that up to him,” Johnson said, referring to Trump.

Control of the House of Representatives is still officially up for grabs, but Republicans appear positioned to keep the majority by a similarly tiny edge that has made it so difficult for them to govern over the past two years.

As of Tuesday afternoon, they had won control of 216 seats, and Democrats had 207. A party needs 218 seats for a majority, and most strategists expect that the GOP will not end up with many more than that.

Trump has already picked Rep. Elise Stefanik of New York, the No. 4 House Republican, to serve as the ambassador to the United Nations, and Rep. Michael Waltz, R-Fla., as his national security adviser.

The developments on both sides of the Capitol reflected how Trump has bent the party to his will, with would-be Senate leaders pitching themselves as best equipped to carry out his agenda and House Republicans clamoring to join his administration.

The contenders for Senate majority leader are Thune, who is currently the No. 2 Republican; Sen. John Cornyn of Texas, who has held several leadership positions in the Senate; and Sen. Rick Scott of Florida, who is seen as the favorite of the party’s right flank.

Trump was expected to visit Capitol Hill on Wednesday morning, ahead of the Republican leadership elections in both the House and Senate.

By Tuesday, the race to replace McConnell, who helped conservatives gain a supermajority on the Supreme Court, went into a form of heated, if genteel, overdrive.

Thune made his case in an opinion essay on Fox News, arguing that Senate Republicans need to fulfill Trump’s promises to voters in order to keep the support of a multiethnic, multiracial coalition that swept him into a second term.

“If we fail to deliver on President Trump’s priorities, we will lose their support,” he wrote. “They have trusted us with their votes. Now we have to roll up our sleeves and get to work.”

He also pitched colleagues on his plans to open up the Senate floor to more debate and amendments and said he would meet regularly with Speaker Mike Johnson.

Cornyn circulated a letter casting himself as the candidate best equipped to overhaul the chamber to get the job done for the MAGA movement.

“In order to make America great again, we must make the Senate work again,” Cornyn wrote to his colleagues. “To that end, we will reinvest in a Senate committee process to drive an aggressive legislative agenda that secures our border, reduces federal spending, boosts our economy, unleashes the nation’s energy potential and reverses bad Biden-Harris policies.”

And Scott promoted endorsements from conservative activists on social media, including arguments that he would work to keep transgender athletes out of women’s sports.

The secret-ballot election will be held Wednesday morning. Retiring senators, such as Mitt Romney of Utah, are not eligible to vote, but senators-elect, such as Tim Sheehy of Montana, are. With Republicans expecting to control 53 seats, the winning candidate must have the backing of a majority of those senators, or 27 votes, to become leader.

The former president has railed against Thune in the past over his refusal to go along with Trump’s attempt to overturn the 2020 election. He has also criticized Cornyn and Thune as “weak and ineffective.”

Both Thune and Cornyn have worked to improve their relationships with Trump. Thune visited Mar-a-Lago in the spring and spoke with Trump just days ago. Cornyn met with Trump twice in recent months and also speaks with him regularly. The two have run quiet, traditional races, working in one-on-one meetings with senators to secure votes, pitching themselves as experienced leaders who can navigate the intricacies of Congress to deliver on Trump’s legislative agenda.

Scott, by contrast, is running to appeal to the right flank of the party — and doing so publicly and online. Many in the establishment wing of the party view Scott’s time leading Senate Republicans’ campaign arm as a failure. He was blamed for a failure to recruit quality candidates, questionable spending practices, and the release of a disastrous policy agenda including tax increases and the phasing out of popular entitlement programs that was quickly repudiated by his colleagues. When Trump urged him to challenge McConnell for Republican leader two years ago, Scott fell well short, receiving only 10 votes.

Most Republican senators have not publicly declared which of the three candidates they support. Privately, some are grumbling about online influencers attempting to pressure them to change their votes.

Senators typically resent outside intervention, even by a president, in their internal affairs, and view it as remarkable that a president would try to handpick their leader.