WASHINGTON (AP) — Republicans have elected South Dakota Sen. John Thune as the next Senate majority leader, completing a momentous shift in their leadership that elevates a top deputy of Mitch McConnell into a key position as President-elect Donald Trump returns to the White House.

Thune, 63, is in his fourth Senate term and has promised to work closely with Trump, despite differences the two have had over the years, and will be a crucial part of the incoming president’s efforts to push through his policy agenda. The two spoke on the phone shortly after Thune was elected, the senator posted on X Wednesday afternoon, adding that “Senate Republicans are excited and ready to get to work” with the incoming president.

Trump later congratulated Thune on his social media platform, Truth Social. “He moves quickly, and will do an outstanding job,” Trump wrote. “I look forward to working with him.”

Thune beat out two other competitors, Sens. John Cornyn and Rick Scott, by gaining majority support from GOP senators in two rounds of secret ballots behind closed doors. Scott was eliminated on the first round and the final vote between Thune and Cornyn was 29-24, according to several people who requested anonymity to discuss the private meeting.

Republicans are replacing McConnell, the longest serving Senate party leader, as they prepare to take majority control of the Senate with the 53 seats they won in last week’s elections. It was the first competitive election for Republican leader in three decades and Senate Republicans’ first regime change since McConnell became GOP leader in 2007.

Thune’s election represents a major shift in the upper chamber’s GOP conference as many senators have been eager to move on from McConnell’s long and powerful reign. But it will also be a complicated test for Thune as he will have to manage a conference that is often divided over policy, navigate Trump’s demands of the legislative branch and secure policy wins for the president as he begins his second term.

“It is a new day in the United States Senate,” Thune told reporters immediately after he was elected. He said his majority will work to toughen border security laws, lower energy costs and overturn regulations they see as burdensome.

“We are excited to reclaim the majority and to get to work with our colleagues in the House to enact President Trump’s agenda,” Thune said.

As the candidates tried to win over individual senators, all of their pitches centered around how close they would be to Trump. That was a more difficult task for Cornyn and Thune, who broke publicly with the former president over his effort to overturn his defeat in the 2020 presidential election and the Jan. 6, 2021 attack on the Capitol. At the time, Thune called Trump’s actions “inexcusable.”

In recent months, though, Thune has worked to smooth over that relationship, visiting Trump at his Florida home and consulting with him on how to implement the incoming president’s agenda. Thune told The Associated Press over the summer that he views their potential relationship as a professional one. If they both won their elections, Thune said then, “we’ve got a job to do.”

As he made his case, Thune has made clear that he will listen to Trump’s demands. When Trump posted on X Sunday that the new leader “must agree” to allow him to appoint Cabinet members and others when the Senate is on recess, avoiding confirmation votes, Thune quickly responded in a statement that the Senate must “quickly and decisively” act to get nominees in place and that “all options are on the table to make that happen, including recess appointments.”