Barrasso Opts to Run for No. 2 in Senate G.O.P. Leadership Shake-Up

Senator John Barrasso of Wyoming, one of the potential top contenders to succeed Senator Mitch McConnell as Senate Republican leader, has decided instead to seek the No. 2 position.

Mr. Barrasso, currently the third-ranking Republican in the Senate, told his colleagues on Tuesday that he was running to be what is officially known as the assistant Republican leader but is informally called the whip. The spot is being vacated by Senator John Thune of South Dakota, who declared this week that he would seek the top job following the decision by Mr. McConnell, the longtime party leader from Kentucky, to step down at the end of the year.

In a letter to fellow Senate Republicans, Mr. Barrasso suggested he would offer a more aggressive style of leadership, and said he hoped his performance in leadership positions in recent years had shown he could deliver.

“One thing that is clear to me is that the Republicans in the Senate need to break from where we are now,” he wrote. “We need change. We need to stand up and fight aggressively for our Republican priorities. We cannot afford missed opportunities.”

His announcement came one day after Mr. Thune, who had already made clear that he intended to try to succeed Mr. McConnell, told home-state media that he was definitely running for the top spot.

“For me, it’s really about trying to be a difference-maker,” Mr. Thune told Dakota News Now in a report published on Monday. “I think I have something to contribute there. I think we’re ready for a new generation of consistent, principled, conservative leadership for Republicans in the United States Senate that empowers our individual members.”

The South Dakota senator faces Senator John Cornyn of Texas, who formerly held the No. 2 job before he was pushed out by term limits, and who declared almost immediately after Mr. McConnell’s announcement last week that he would be a candidate for Republican leader. Mr. Cornyn also promised to run a more inclusive leadership operation after so much power has been centralized under Mr. McConnell during his record-breaking run as leader.

“We will improve communication, increase transparency, and ensure inclusion of every member’s expertise and opinion,” Mr. Cornyn said.

With the shake-up coming in the leadership ranks, Senator Tom Cotton, Republican of Arkansas, has been informing colleagues since last week that he intends to run for the No. 3 position as chair of the Senate Republican Conference, the post now held by Mr. Barrasso.

The election to replace Mr. McConnell and choose other members of the leadership is set to be conducted some time after the November elections and will include newly elected senators, though some have called for Mr. McConnell to step aside sooner to spare his party a drawn-out intramural fight.

The amount of time before the contest means others could get into the race. Some Republican senators on the far right have encouraged Senator Rick Scott of Florida to jump in, and Senator Steve Daines of Montana, who is overseeing the campaign effort for Senate Republicans, has also been mentioned as a possible contender.