BOSTON — As he signed into law new protections for insurance coverage for women’s birth control in Massachusetts, Republican Gov. Charlie Baker stood shoulder to shoulder with about three dozen supporters of the bill, nearly all of them Democrats, in the Statehouse library.

Speaker after speaker, including the head of Planned Parenthood in Massachusetts, thanked and praised Baker for backing the legislation and reproductive rights for women in general. Baker did not flinch, and at times applauded briskly, when speakers castigated Republicans in Washington who have targeted birth control coverage and funding for Planned Parenthood.

The scene Monday was yet another example of Baker’s uncomfortable relationship with the national GOP establishment. But it was also a reminder of the difficulty Democrats likely face in dislodging the governor from office in the 2018 election, regardless of how unpopular the Republican brand may be in Massachusetts.

“He’s not a hardcore partisan,” said Peter Ubertaccio, an associate professor of political science at Stonehill College who follows Massachusetts politics closely. “It’s going to be a real challenge for the Democratic nominee. There will be a number of Democrats who will stay neutral or give their nominee only tepid support.”

The losses suffered by the GOP on Nov. 7 in governor’s races in Virginia and New Jersey, and other local contests around the country — along with low public approval ratings for President Donald Trump and the Republican-controlled Congress — has buoyed Democrats’ hopes for a strong turnaround at the polls next November.

But in Massachusetts, where Democrats hold every congressional seat and a veto-proof majority in the Legislature, Republican Baker may well be insulated by his own personal popularity and a reputation for bipartisanship that appeals to independent-minded voters and moderate Democrats alike.

Baker has said he did not vote for Trump, or anyone else on the presidential ballot. Since January he has separated himself from the White House and many congressional Republicans on issues ranging from health care to immigration, gun control and transgender rights. Unlike GOP candidates in many other states, Baker has less reason to worry about angering a conservative “base” which is relatively small in Massachusetts, though Trump did win last year’s Republican primary convincingly.

Baker has yet to formally announce his intention to seek a second term but had amassed nearly $7 million in his campaign account through mid-November.

The three announced Democratic candidates are Jay Gonzalez, the states’ former budget chief; Robert Massie, an environmental activist; and Newton Mayor Setti Warren. All lack widespread name recognition and trail far behind the incumbent in early polling.

The Democrats, Ubertaccio said, will likely seek to poke holes in Baker’s image as a top-flight manager by flagging continued state budget woes among other things, and capitalize more generally on anti-Republican sentiment by offering “a long term vision of the state different form Charlie Baker and more in line with Democratic priorities.”

Democratic party leaders have recently accused Baker of hypocrisy for endorsing down-ticket Republican candidates with more conservative views on social issues. State party chairman Gus Bickford pointed to Baker’s backing of Fitchburg City Councilor Dean Tran, the GOP nominee in a Dec. 5 special state Senate election.

Tran is on record as opposing any state funding for Planned Parenthood and against some transgender rights laws.

“The governor can’t have it both ways,” said Bickford.

Speaking to reporters after signing the birth control coverage bill, Baker was unapologetic for his endorsement of Tran, citing an accomplished record in municipal government.

“I’ve supported candidates that I don’t agree with on a lot of issues,” said Baker. “I don’t expect to agree with everyone on everything all the time. I believe it’s OK to disagree.”