Massachusetts Gov. Charlie Baker. (Steven Senne/AP)

There's a saying in Massachusetts political circles: A Republican in this state is a Democrat pretty much anywhere else.

Massachusetts Gov. Charlie Baker would probably fall into that category. The Republican health-care executive was elected governor in 2014 on a platform of fiscal conservatism, favoring abortion rights and same-sex marriage. He was the first Republican gubernatorial candidate the Boston Globe endorsed over a Democrat in 20 years, and today he just might be the most popular governor in the United States, with approval ratings that have measured upward of 70 percent.

But Baker's moderate political worldview has been both a blessing and a challenge for him, especially in a time of upheaval within his own party. He's in the unenviable position of having to straddle his party's rightward lurch on the national stage while maintaining control of a deep-blue state.

Baker's delicate balance came to a head this week. On Tuesday, Massachusetts GOP primary voters overwhelmingly supported Donald Trump by a margin of 31 points, giving Trump his most definitive Super Tuesday win. On Wednesday, though, Baker told reporters he wouldn't vote for Trump in November.

This was also, we would note, a few days after the man Baker had endorsed for president, New Jersey Gov. Chris Christie (R), endorsed Trump.

Massachusetts has had Republican governors before, of course. (One of them denounced Trump in pretty strong terms on Thursday.) But the fact that Baker's time in office and his popularity coincide with what's amounting to a crisis in his party makes him one of the most interesting governors in the United States right now.

Here's more about Baker and how he's navigating the Trump phenomenon in his state so far:

His mom was a Democrat, his dad a Republican

And he'll tell you that every chance he gets, says Boston University political science professor Virginia Sapiro. On the campaign trail, he liked to call it a "mixed marriage."

But Baker is careful not to present himself as a mashup of his parent's ideologies, lest he seem weak. Rather, Sapiro said, he portrays himself as someone who holds his own political views quite firmly but learned from his childhood dinner table conversations how to get along with the other side.

"The big lesson was that you can disagree without being disagreeable," Baker said on the campaign trail back in 2010, the first time he ran for governor. (He lost that race to incumbent Democrat Deval Patrick by six points.)

He just claimed victory in his own Republican Party battle

Baker's kumbaya approach to politics hasn't spared him intra-party drama with the tea party.

In his 2014 election, some grassroots conservatives in Massachusetts went out on a limb and supported Baker. But this year, Baker turned against that faction when he actively campaigned for moderate Republicans running for the Republican State Committee, the state party's governing body.

The Boston Globe's Frank Phillips reports that Baker raised $300,000 and endorsed candidates in almost all of 80 seats up for grabs in the Tuesday primary. His active campaigning appears to have paid off; 51 of Baker's allies won or retained seats on the committee, swinging power on the committee in his direction.

Baker's win may have come at price of damaged relations with his party, though. "They started an unnecessary war within their own party," one conservative committee member, who won despite Baker's efforts, told the Globe.

"Charlie Baker wants to purge the state committee of the Trump voters and assorted other bitter clingers," complained conservative Boston Herald columnist Howie Carr.

How Baker handles the fallout will probably shape his relationship with his party for the rest of his tenure as governor.

He hasn't had a major misstep -- yet

When the Globe endorsed Baker over his Democratic opponent, Attorney General Martha Coakley, its editorial board acknowledged "a Baker governorship may have its awkward moments." On the trail, for example, Baker apologized after he called a female reporter "sweetheart."

So far, he's largely avoided negative headlines in office. He did say he was "surprised" when Christie endorsed Trump, but he added that Christie is his own man.

Baker is strategic about when he wants to play politics and when he keeps quiet, Sapiro said. He'll jump into the fray when he sees clear benefits for himself.

For example, Baker's aides pointed out to the Globe that the governor had repeatedly said he wouldn't vote for Trump in the primary -- but Baker managed to keep that fact relatively quiet until after Tuesday's primary.

He's focused on courting independents

All this makes Baker's decision to stand firmly in the anti-Trump camp a day after his state voted overwhelmingly for Trump all the more interesting.

It's likely that his campaigning against conservatives and his rebuke of Trump is an acknowledgment that Baker was always going to clash with the right wing of his party. And to some degree, Baker can afford that fight. Where else in Massachusetts are Republicans going to go?, Sapiro asked.

Baker seems more intent on maintaining the peace with independents and even Democrats. Which makes sense, since he's the governor of Massachusetts.

But in the era of Trump, even that might prove to be difficult. Trump won the state with a wide margin of independents -- the same voters Baker will depend on in his assumed reelection bid in 2018.

(Although we should note Massachusetts's ranks of independents are by no means monolithic. Nearly 2.3 million voters are registered as unenrolled, almost twice as many registered Democrats and nearly five times as many registered Republicans.)

It remains to be seem if Baker suffers fallout among Massachusetts Republicans and independents for his recent stand against the conservative wing of his party. And a lot can and probably will happen to Baker before his 2018 reelection bid.

But for Massachusetts's Republican governor, this near-singular focus on Trump probably can't end soon enough.