And we have our first official reversal! Illinois’ Republican Sen. Mark Kirk, currently in the midst of a competitive re-election campaign, withdrew his support of Donald Trump on Tuesday.

Given my military experience, Donald Trump does not have the temperament to command our military or our nuclear arsenal. — Mark Kirk (@MarkKirk) June 7, 2016

While Kirk’s tweet cited Trump’s (in)ability to be commander in chief, a longer statement released by his campaign focused on the ongoing controversy over Trump’s recent criticism of Gonzalo Curiel, an Indiana-born judge who Trump maintains is biased against him because his parents were born in Mexico:

I have spent my life building bridges and tearing down barriers–not building walls. That’s why I find Donald Trump’s belief that an American-born judge of Mexican descent is incapable of fairly presiding over his case is not only dead wrong, it is un-American.

As the Presidential campaign progressed, I was hoping the rhetoric would tone down and reflect a campaign that was inclusive, thoughtful and principled. While I oppose the Democratic nominee, Donald Trump’s latest statements, in context with past attacks on Hispanics, women and the disabled like me, make it certain that I cannot and will not support my party’s nominee for President regardless of the political impact on my candidacy or the Republican Party.

It is absolutely essential that we are guided by a commander-in-chief with a responsible and proper temperament, discretion and judgment. Our President must be fit to command the most powerful military the world has ever seen, including an arsenal of thousands of nuclear weapons. After much consideration, I have concluded that Donald Trump has not demonstrated the temperament necessary to assume the greatest office in the world.

In an interview with CNN, Kirk said he plans to write in former CIA director David Petraeus’ name on his presidential ballot come November.



Back before Trump became his party’s presumptive nominee, Kirk said that he would support him if he did ultimately lock up the nomination. More recently, Kirk had quibbled with a few of Trump’s positions, but made it clear he was willing to overlook any differences of opinion in the name of his own re-election chances. “Donald Trump is kind of a riverboat gamble,” he told CNN in May. “He won the Illinois primary, in this case we have seen the Republican vote up and the Democratic vote down, so it looks like it’s a net benefit.”

According to the Cook Political Report’s most recent ratings—published back in March—Kirk’s Illinois race against Rep. Tammy Duckworth is one of seven toss-ups on the Senate electoral map this fall. On Monday, Duckworth ratcheted up the pressure on Kirk to denounce Trump, warning that he and his fellow Republicans deserved “to be judged harshly” for failing to publicly rebuke him.

Kirk has broken with his party before—notably by suggesting that his fellow Senate Republicans should treat Supreme Court nominee Merrick Garland as something beyond a political prop—but his willingness to walk away from Trump stands out given all the other Trump-skeptical Republicans who have stuck by the presumptive GOP nominee even while trying to distance themselves from his remarks. House Speaker Paul Ryan, for example, decried the Donald’s comments as “completely unacceptable” and a “textbook example of a racist comment” earlier on Tuesday, but then went on to stress that he was still backing his party’s standard-bearer.

Whether Kirk’s Senate colleagues who are locked in their own re-election fights will follow his lead or not is an open question. Given what we’ve seen so far, my bet is their decision will probably come down to the same thing Kirk’s did last month, and no doubt did again today: Will it help or hurt their chances of keeping their jobs?

Read more of Slate’s coverage of the 2016 campaign.