President Donald Trump will soon find out whether he has a new wild card to worry about in the Senate after helping send John Cornyn (R-TX) into an early retirement.Cornyn on Tuesday became the second incumbent to lose his primary to a Trump-backed challenger, handing Senate leadership another lame duck with no incentive to back Trump or his legislative agenda. The first was Sen. Bill Cassidy (R-LA), who quickly made clear he would use his political freedom to criticize Trump on everything from the war in Iran to the Justice Department’s $1.8 billion “anti-weaponization” fund.Cornyn’s immediate message after he lost to Texas Attorney General Ken Paxton was conciliatory, telling reporters gathered for his concession speech that he would support the Republican ticket this fall. And Trump, too, sought to tamp down tensions with Cornyn, calling him a “friend” and lauding his decadeslong career in the Senate.

But if recent history is any guide, Cornyn’s retirement instantly makes him an unreliable vote for the White House, and Cassidy is not the president’s only problem.

Sens. Thom Tillis (R-NC) and Mitch McConnell (R-KY) fit into the category of retiring senators who have occasionally, and sometimes vocally, broken with the president. Several other Republicans have an independent streak but aren’t up for reelection this cycle. On any party-line vote, Senate leadership can afford to lose only three Republicans.