Sen. Jeff Flake (R-AZ) is the latest in a long line of Republicans to express dismay over Donald Trump's attacks on the judge presiding over the Trump University class-action lawsuit.

Flake, according to AP, says the latest controversy involving the presumptive GOP nominee could "spur" a challenge at the GOP convention.

He expressed the belief that Republicans cannot win the White House with Trump as the nominee. 

Let's face it: meet the old Trump, just like the new Trump. We've got what we've got. That's not somebody who can win the White House. Where there's no talk of a convention challenge or anything else, this might spur it.

Flake endorsed Marco Rubio for the GOP nomination back in February. 

Meantime, Sen. Mark Kirk (R-IL), in an "un-endorsement," now says he cannot support Trump in light of the new controversy.

Kirk, who faces a tough re-election contest in the fall, said Trump "has not demonstrated the temperament necessary" to be president.

House Speaker Paul Ryan (R-WI) said today that Republicans must "absolutely disavow" Trump's attacks on Judge Gonzalo Curiel.

On Fox News Sunday, former House Speaker Newt Gingrich, said it was a big mistake for Trump to suggest that the Indiana-born Curiel is biased against him because he's of Mexican descent.

"It was one of the worst mistakes Trump has made. Inexcusable," said Gingrich, who has been advising Trump in the campaign.

Trump called Gingrich's remarks "inappropriate" and defended himself in a Factor interview last night, arguing Curiel has been unfair to him.

"I'm going to do great with the Mexican people, 'cause I provide jobs, so I don't care about Mexican. But we're being treated very unfairly."

Hacker Announces Death of Roger Goodell from NFL's Twitter Account

'It's Not Fair': Transgender Student's Success in Girls Track Causes Backlash

State Dept Aide 'Can't Recall' Sending Email About Hillary's Private Server