Governor Charlie Baker of Massachusetts and his lieutenant governor, Karyn Polito, announced this month that they would not seek re-election in 2022. It’s another nail in the coffin of moderate Northeastern Republicanism.

That used to be a significant strand within the Republican Party, but it is increasingly rare. Mr. Baker and Ms. Polito were among the few remaining exceptions. Their impending departure tells a political story with implications beyond the Bay State.

Even the northeastern Republicans themselves have been fleeing south and west.

It’s been happening for years. Mitt Romney, a Baker predecessor as governor of Massachusetts, was the GOP’s presidential nominee in 2012. He now represents Utah in the Senate.

Donald Trump, a New Yorker when he was elected president in 2016, has since relocated to Florida.

The Bush political dynasty began with Senator Prescott Bush of Connecticut. President George H.W. Bush spent vacations on the Maine coast but moved his family base to Texas, where President George W. Bush was governor. Jeb Bush was governor of Florida.

If leaving the region isn’t an option, there’s always the possibility of leaving the political party. Michael Bloomberg, elected mayor of New York as a Republican, left to become an independent and then ran for president as a Democrat. William F. Weld, who preceded Messrs. Romney and Baker as a Republican governor of Massachusetts, joined the Libertarian Party and ran for president that way.

One-party rule is a recipe for corruption and runaway government spending, so even those who don’t find the Republican party or the policies of its Northeastern strain particularly attractive have a stake in at least some sort of competition in the market for political leadership.

In places like New York and Massachusetts, and to some extent in the Democratic Party nationally, the ideological and political competition that used to exist between centrist Republicans and regular Democrats increasingly has migrated to the Democratic Party itself.

Progressives or far-left Democratic candidates compete against those who at least publicly express more moderate views. When progressive policies fail, as in Bill de Blasio’s New York City, voters install a more centrist-appearing Democrat rather than a Bloomberg or a Mayor Giuliani.

With the coming departure of Mr. Baker and Ms. Polito, remaining Northeastern Republicans include the governor of New Hampshire, Christopher Sununu; the governor of Vermont, Phil Scott; and a senator from Maine, Susan Collins.

The six New England states are so thoroughly Democrat-dominated that they currently have not a single Republican member of the House of Representatives. The current partisan split in the Massachusetts State Senate is 36 Democrats, 3 Republicans, and one independent. There are university faculties with more ideological diversity than that.

If politicians with the profile of Messrs. Baker and Romney or Ms. Collins were entering politics today, they might have brighter futures in New England as centrist Democrats. Mr. Baker’s farewell laundry list of accomplishments — offshore wind energy, “dramatically increased funding for our schools,” better rural broadband internet availability — sounds little different from what a Democrat would brag about. The exception is Mr. Baker’s boast line about how “we cut the income tax to 5 percent.”

The differences between Northeastern Republicans and other ones extend beyond policy to tone. Mr. Baker talked about how a “bipartisan approach, where we listen as much as we talk, where we focus our energies on finding areas of agreement and not disagreement, and where we avoid the public sniping and grandstanding that defines much of our political discourse, allows us to make meaningful progress on many important issues.”

There’s some truth to that, but there’s also some spin. If the progress had really been as meaningful as Mr. Baker describes it, he and Ms. Polito would be coasting to re-election or anointing a chosen Republican successor, rather than leaving with no clear heir.

Perhaps it’s too much to ask of a Charlie Baker, or a George Pataki or a Mitt Romney, to govern a state and on top of that also to chart an ideological and political path forward for a civil, non-extremist conservatism that inspires both elite donors and ordinary voters.

Yet if the Republican Party is going to return to its heyday of the 1984 Reagan landslide, it will need to get better than it has been at attracting independents and crossover Democrats like those who twice elected Mr. Baker in Massachusetts.