"The American Presidency is an office that goes beyond just politics," Bush wrote. "It requires of its occupant great fortitude and humility and the temperament and strong character to deal with the unexpected challenges that will inevitably impact our nation in the next four years. Donald Trump has not demonstrated that 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."
Earlier on Friday, Sen. Lindsey O. Graham (R-S.C.) sent reporters a statement explaining his own reasons for rejecting Trump.
"I absolutely will not support Hillary Clinton for President," Graham wrote. "I also cannot in good conscience support Donald Trump because I do not believe he is a reliable Republican conservative nor has he displayed the judgment and temperament to serve as commander in chief."
The senator, who has backed every iteration of immigration reform and argued for Republicans to embrace it, also told CNN that Trump was making it impossible for the party to win Latino votes.
"Eating a taco is probably not going to fix the problem we have with Hispanics," Graham said, referring to a viral Trump tweet from Thursday afternoon. "Embracing Donald Trump is embracing demographic death."
Graham, who ran for president in the 2016 primaries but pulled out before any votes were cast, was frustrated in multiple attempts to stymie Trump. The network rules that split debates into main stages and "undercards" relegated him to low-rated and occasionally low-energy contests, unable to confront the mogul face-to-face. After leaving the race, Graham endorsed Bush.
Bush's fight with Trump was longer-lasting and more prominent than Graham's, but just as doomed. In the fall of 2015, he began attacking Trump as a "bully" and a "chaos candidate" who was unfit to serve. But to the surprise of some of the party's largest donors, who assumed that the most successful dynasty in Republican politics could unify the party, Bush's unfavorable numbers rocketed ahead of Trump's.
The struggling Bush became more critical of the front-runner. In December, he said he might not stick to a pledge to support the Republican nominee if that meant backing Trump. After a disastrous fourth place finish in South Carolina — where former president George W. Bush joined his brother and Graham at a rally — Bush quit the race.
After Sen. Marco Rubio (R-Fla.) was defeated, Graham and Bush made a shocking endorsement in the hopes of creating an anti-Trump front. Both backed Sen. Ted Cruz (R-Tex.), whom Graham made no secret of disliking.
"If you killed Ted Cruz on the floor of the Senate, and the trial was in the Senate, nobody would convict you," Graham joked at a charity dinner. Weeks later, appearing at a fundraiser with Graham near the American Israel Public Affairs Committee policy summit, Cruz joked that it was his first endorsement from someone who wanted him dead.
Bush did even less for Cruz. In an interview with The Washington Post last month, Graham did not feign excitement about his options. He was cool to the idea of a contested convention picking a "white knight," or even Ohio Gov. John Kasich (R), who he thought was the party's strongest nominee. "There would be a revolt on the floor of the convention," Graham said.
In his Friday statement, Graham said he would be skipping the convention in Cleveland. Trump responded with his own statement, a vitriolic paragraph of derision.
"I fully understand why Lindsey Graham cannot support me," the presumptive Republican nominee for president said. "If I got beaten as badly as I beat him, and all the other candidates he endorsed, I would not be able to give my support either. Every time I see Lindsey Graham spew hate during interviews I ask why the media never questions how I single handily destroyed his hapless run for President. As a candidate who did not receive 1 percent in his own state — compared to my victory at nearly 40 percent with many others in the race — he has zero credibility. He was a poor representative and an embarrassment to the great people of South Carolina. Judging by the incompetent way he ran his campaign, it is easy to see why his military strategies have failed so badly — we can’t even beat ISIS!"