Baker has been a lifelong Republican and says he can't remember the last time he didn't vote for his party's nominee for president.
"I'm a big tent Republican," Baker told reporters after an event in Jamaica Plain where he helped stock Jamaica Pond with rainbow trout.
"I supported a lot of folks with a lot of points of view. But as I’ve said from the beginning of this race, I have concerns about Mr. Trump’s temperament. Some of the things he has said about women and about Muslims and about religious freedom — I just can’t support."
What Baker will do concerning the top of the ticket, he's not sure. But don't expect him to vote for the likely Democratic nominee.
"I sincerely doubt I’ll be voting for Hillary Clinton either," Baker said, citing what he called the former secretary of state's "believability issues."
Early in February, Baker came out in support of New Jersey Gov. Chris Christie. But less than a week after that endorsement, Christie dropped out of the race after his sixth place finish in the New Hampshire primary.
As the campaign went on, Baker made no secret of his disdain for Trump, and he expressed hope that another candidate to his liking might emerge either from the pack or from a contested convention. But with Trump the de facto nominee, Baker says he will divert his attention away from the national race.
"It means I’m going to focus my time on my day job and some of the races that are going on here in the commonwealth," Baker said. "There are a lot of really good folks running for state rep and state Senate and that’s where I’m going to spend my time and my energy."
Specifically, Baker's political advisor Jim Conroy said in an email, the governor, "will support with formal endorsements, appearances in the district, and fundraising."
State Rep. Geoff Diehl, Trump's Massachusetts co-chair, is hoping Baker may have a change of heart.
"Maybe he should consider keeping the door open to Donald Trump if he becomes president," Diehl said. "It would be important for the citizens of Massachusetts. You know I certainly am going to make sure I do what I can help Donald Trump win and be able to contribute to the state. Hopefully, there's a chance for reconsideration at some point, but that's his choice."
This segment aired on May 4, 2016.