The most powerful person on Democrat-heavy Beacon Hill may be the lame-duck Republican governor

Governor Charlie Baker is in the driver's seat on Beacon Hill.David L. Ryan/Globe Staff

He’s a lame-duck Republican in a deeply blue state with the end of his term in view. Yet, Governor Charlie Baker may also be the most powerful person on Beacon Hill right now.

Thanks to a legal quirk, a quickly evaporating calendar, and its logjam of unfinished work, the Legislature has ensured Baker will — again — wield extraordinary influence over what becomes law despite both chambers’ Democratic supermajority, this time in the governor’s final session on Beacon Hill.

The dynamics could have major ramifications for closely watched and complicated legislation, from proposals expanding reproductive health rights and banning new prison construction to a suite of others collectively dispensing with tens of billions of dollars.

The Legislature has to complete its formal lawmaking by the end of the month. But Baker is allowed 10 days to act on any legislation that reaches his desk, meaning he can hold onto any bill that reaches him between now and July 31 until after lawmakers break for the session.

Because of an additional twist, Baker could also effectively pick and choose which policies survive within a $52.7 billion budget proposal currently on his desk. And while much of a $1 billion tax relief package lawmakers are trying to finish ahead of their July 31 deadline reflect Baker’s own priorities, he’ll have final say on whether the pork and policy riders lawmakers pass with it cross the finish line.

“We knew the deadline was in there. We worked to get it done by the deadline, [and] we didn’t do it,” House Speaker Ronald Mariano said of ceding power to Baker in the session’s final days. “So now we have to live with those consequences.”

To be sure, Baker and Democratic leaders have long enjoyed a good working relationship, helping eliminate the type of political fistfights that define Washington, D.C.

But the timeline could nevertheless tie lawmakers’ hands in overriding Baker’s objections to entire pieces of legislation or line items within spending bills.

In the case of the budget proposal, which Baker must act on before month’s end, he has the option of sending policy sections back with recommended changes instead of outright vetoing them. Should lawmakers then reject his proposed amendments before they finish formal sessions, the 10-day clock restarts — giving Baker the chance to then issue vetoes on items he disapproves of when lawmakers have little recourse to respond beyond calling a special session.

In last year’s spending plan alone, of the 27 sections he volleyed back to lawmakers, 25 came with amendments and just two were outright vetoes, according to the Massachusetts Taxpayers Foundation.

“I don’t expect unnecessary gamesmanship in the name of interfering with the legislative agenda. That’s not the way the governor has approached policy during his entire tenure,” said Evan Horowitz, executive director of the Center for State Policy Analysis at Tufts University. “But he’s also not afraid to ask — in the name of his own stated preferences and beliefs — about what accomplishes the best policy.”

Of course, it’s a situation Democratic leaders have helped thrust upon themselves. They still have at least eight conference committees negotiating details of legislation, and will likely need another to reconcile a multibillion-dollar economic development bill. They also still need to formally send a more than $5 billion bond bill to Baker.

Within that is language establishing a five-year ban on the construction of new correctional facilities or the expansion of current ones across the state.

The proposal includes a carve-out for “accommodating” a transfer of inmates because another facility is closed, but Baker administration officials have raised concerns about a moratorium potentially tying their hands. A state-hired consulting firm also concluded last month that the state’s only women’s prison needs to be replaced, and that the state should build a $40 million, 150-bed medium security facility.

What exactly Baker could seek to deny, stall, or reshape in the coming weeks is not entirely clear. During his nearly eight years in office, he has been famously tight-lipped about his stance on pending legislation rushing toward his desk, often offering only veiled opinions or, more likely, a polite declination to comment.

That’s true this time, too.

In crafting legislation in response to the Supreme Court overturning the landmark Roe v. Wade decision, lawmakers are at odds over language regulating later-term abortions, specifically whether to allow them in cases of “severe” fetal anomalies.

In pushing their version — which did not include that wording — Senate leaders have nodded to a potential gubernatorial veto given Baker’s opposition to a part of a 2020 measure that allowed abortions after 24 weeks in the case of a “lethal” fetal anomaly.

Baker supports abortion rights, and portions of the pending bill reflect an executive order he signed that sought to protect providers here. But when asked Thursday during a Boston Public Radio interview about his stance on the latest debate, Baker declined to weigh in, arguing it’s difficult to respond until something officially reaches him.

Co-host Jim Braude quickly questioned whether that’s helpful.

“Instead of [lawmakers] going through a tortured process, why don’t you say to them what you’re willing to do, so they’re on notice that if they do X, you’re gonna sign the damn thing, and if you do Y, ‘I’m not going sign the thing?’” Braude asked. “Isn’t that a more sane way to go about legislating?”

Baker, however, didn’t relent.

“I have never thought that on points of disagreement — particularly intense ones like this — that me picking a side actually helps,” he said. “I think it probably hurts with respect to their ability to get to ‘yes.’”

Baker, of course, has leveraged the calendar before to leave a dramatic imprint on what “yes” looks like.

At the end of an elongated session in 2021, he blocked new protections for renters and a proposed fee hike on Uber and Lyft rides in two omnibus borrowing bills. He also successfully pressed lawmakers to remake a policing bill in the 11th hour that legislative leaders had spent months composing.

Back in 2018, he, too, used the clock in his favor to amend and return a bill to lawmakers the day after formal sessions ended that determined how the state regulated Airbnb and other short-term rentals. It wasn’t until nearly five months later that a compromise version surfaced — with a version of Baker’s suggested changes — and lawmakers quickly passed it through sparsely attended sessions.

There’s also another problem with lawmakers leaving so much work until the final days of a 19-month session, Horowitz said: Real, robust debate on complex legislation can be a casualty.

“It’s a failure,” he said, “across a number of dimensions.”

Samantha J. Gross of the Globe staff contributed to this report.