New York is a pretty Democratic state. There’s something like a 2-1 Democratic registration advantage. The vote in Presidential elections is predictably lopsided. We’ve got a popular Democratic Governor, and two Democratic Senators. Our House delegation is overwhelmingly (though not exclusively) Democratic. And the Republican Party’s fortunes keep dropping. Their last bastion of power, until recently, was the State Senate. Then they lost that.

Or so it seemed. Now, they’ve been brought back from the dead by a group of Independent Democrats, who have formed a coalition with the Republicans to keep the Senate out of exclusively Democratic hands:

With the new coalition, the leaders of the Republican and the Independent Democratic conferences would have “joint and equal authority” over bills that the Senate takes up, committee assignments, appointments and state budget negotiations. Albany’s famous “three men in a room” — the governor, the Assembly speaker and the Senate majority leader, who negotiate the state budget and major legislation — would become a quartet.

Mr. Skelos and Mr. Klein would also take turns, alternating every two weeks as temporary president of the Senate, a position defined in the State Constitution that is next in the gubernatorial line of succession after the lieutenant governor.

In an interview, Mr. Klein said Senate Republicans had committed to allowing floor votes on a number of critical measures for which Democrats had unsuccessfully pushed when Republicans had an outright majority.

“Working with the governor and our colleagues, I know that we will pass some major progressive reforms, such as an increase to the minimum wage, a reform of stop-and-frisk and serious campaign finance reform,” Mr. Klein said. “I’m extremely confident that these issues will come to the Senate floor for a vote and I fully expect them to pass the Senate.”

Basically, by bolting from their party, this handful of Democrats have gained control of the Senate. The Republicans can’t piss them off, or they’ll just go back home to their original party, leaving the Republicans with no power at all. And the Democrats can’t punish them unless they achieve such a massive victory at the polls that they achieve a majority without counting the defectors. Meanwhile, with this much leverage, they should be able to take very good care of their own constituencies, assuring that they don’t have to worry about personally losing an election.

And Governor Cuomo seems perfectly happy with this outcome, and for good reason. On the one hand, it means the Republicans will have to agree to anything that gets passed – which makes it harder for them to attack him. On the other hand, it means he doesn’t have to play bad cop restraining the more extravagant impulses of his own party – he can get the Republican Senate to do that for him. Either way, he wins.

I’m surprised we don’t see more of this kind of behavior in states that are politically far from the national median. In you’re in an elastic state like New Hampshire or Colorado, the odds are the parties are going to rotate in power, so there are multiple opportunities to punish defectors and a limited amount of leverage to be gained by forming a centrist splinter group – and considerable advantage to playing the role of a loyal partisan. But where a state leans heavily toward one-party rule in the legislature, backbenchers have little opportunity for advancement, and a centrist breakaway group could have considerable leverage.

Of course, it only works if the minority party knows it’s going to remain in the minority essentially forever, and is therefore willing to settle for moderating the majority’s tendencies rather than opposing them outright in the hopes of setting the agenda after a future election that brings them to power. But isn’t that a reasonable description of reality for, say, the California Republican Party?

Parties are vehicles for identity-expression. That’s why these Independent Democrats are still calling themselves Democrats, in coalition with Republicans, rather than just switching to the Republican Party. They’re just sufficiently self-interested and/or public-spirited to be willing to break party discipline to form a cross-party coalition. But isn’t that also a reasonable description of the centrist wing of, say, the California Democratic Party?

Obviously, every legislature and every state is a unique snowflake, but I’m still curious why we don’t see more of this kind of behavior in states as dominated by a single party as New York is. It’s part and parcel of my puzzlement that third parties always seem more enthusiastic about the long-shot of capturing the Executive, when there would seem to be lower-hanging fruit running for the legislature.