Washington(CNN) Jeb Bush said Friday that he will not vote for Donald Trump in November, joining a list of Republican Party luminaries who will not back the party's presumptive nominee.
"In November, I will not vote for Donald Trump or Hillary Clinton, but I will support principled conservatives at the state and federal levels, just as I have done my entire life," the former Florida governor wrote in a statement published on his Twitter and Facebook accounts. "For Republicans, there is no greater priority than ensuring we keep control of both chambers of Congress. I look forward to working hard for great conservatives in the Senate and House in the coming months."
Trump has "not demonstrated" the necessary "temperament or strength of character. He has not displayed a respect for the Constitution. And, he is not a consistent conservative. These are all reasons why I cannot support his candidacy," Bush said.
Trump responded to Bush at an afternoon rally in Omaha, Nebraska, saying, "No, I won't talk about Jeb Bush. I will not say, I will not say that he's 'low energy,'" Trump said, reviving his memorable nickname for the former Florida governor. "I will not say it. I will not say it."
Bush's announcement marks a reversal from Bush's pledge to support the nominee, even if it turned out to be Trump.
"I will support the Republican nominee no matter who he or she is," Bush told CNN in February when asked about Trump. "I've done it my whole entire life. I've signed a pledge to do it. I'll do it."
Read: Bush vows to back GOP nominee
Bush joins his former rival Lindsey Graham in refusing to vote for either Trump or Clinton. The senior South Carolina senator told CNN's Dana Bash Friday: "I don't think he's a reliable Republican conservative. I don't believe that Donald Trump has the temperament and judgment to be commander in chief. I think Donald Trump is going to places where very few people have gone and I'm not going with him."
Bush told CNN last month he will skip the party's convention in Cleveland this summer. He is part of a growing list of veteran Republicans, including Graham, both Presidents Bush, Mitt Romney, John McCain and others, now declining to attend.
Read: Lindsey Graham won't vote for Trump or Clinton in 2016
Also, House Speaker Paul Ryan said Thursday he's "just not ready" to support Trump, becoming the highest elected Republican official to raise concerns about Trump since he became the party's likely standard-bearer this week.
In an interview with CNN's Jake Tapper, Ryan said he wants Trump to unify "all wings of the Republican Party and the conservative movement" and then run a campaign that will allow Americans to "have something that they're proud to support and proud to be a part of."
Read: Paul Ryan: 'I'm just not ready' to back Donald Trump
"And we've got a ways to go from here to there," Ryan said.