Blame John Boehner. Feel sorry for Boehner, sure — he is a decent man, a willing dealmaker overseeing an unruly caucus, and I’m being kind with that adjective. But blame him, too.

If — and, as is looking increasingly likely, when — the country hurtles over the “fiscal cliff,” it will be in part because the House speaker abruptly decided to upend negotiations with the White House.

Earlier this week, the two sides appeared to be on the verge of a deal. To Boehner’s credit, and more on this later, he had gone a remarkable distance in President Obama’s direction. Suddenly, instead of spending precious time hammering out final details, Boehner shifted to what he called “Plan B.” This made sense only if the “B” stands for blow-up. Which is exactly what happened Thursday night, when Boehner was forced to call off a scheduled House vote on his plan because it “did not have sufficient support from our members to pass.”

Under Plan B, the Bush tax cuts would have been extended, except for households making more than $1 million a year. So Republicans were asked to yield on what once seemed unthinkable, agreeing to raise not only tax revenue but also tax rates.

They would take these tough votes — and for what? A plan that raises taxes (Republican anathema), fails to cut spending (Republican dogma) and does not avert a noxious (especially to Republicans) part of the cliff, the sequester of defense spending.

All of which may help explain Plan B’s astonishing demise.

White House officials were mystified by Boehner’s attempt to maneuver in the first place. Perhaps, they thought, Boehner felt he needed to gum up the works with Plan B to strengthen his bargaining position with the president. Perhaps he felt he needed to convince reluctant Republicans that the deal he was cooking up with the president is the best that can be achieved.

Or perhaps, and this may be the most likely after Plan B’s failure, he, once again, cannot produce the votes for the grand-enough bargain.

Before the non-vote, congressional Republicans insisted that Boehner was forced to switch course because the two sides were further apart than the White House asserted. While the differences could be narrowed, they argued, the time had run out to finalize a deal before the new year.

In the meantime, Republicans said, they were obligated to come up with a solution to avert tax hikes on the vast majority of Americans. If Senate Democrats weren’t willing to start the increases at $1 million — a level Republicans were happy to point out was once endorsed by several top Democrats — they could come up with an alternative.

This would have been more persuasive if the time necessary to ping-pong such a deal back and forth between the two houses wasn’t at least as long as the time necessary for approving a deal negotiated by the president and the speaker. Or if parallel negotiations on the grand-enough bargain were continuing.

Indeed, Plan B seemed aimed more at shifting blame as the cliff arrives than at solving the problem. What suddenly changed between Monday, when talks were proceeding, and Tuesday, when Boehner shifted precipitously to Plan B?

As the fiscal-cliff talks have progressed, way too slowly, I have pointed fingers at both sides for intransigence. Then came signs of remarkable progress.

Boehner gave on both revenue (now $1 trillion) and rates (now letting rates rise for those earning more than $1 million). The White House gave on revenue, rates and entitlements. It reduced its revenue demand to $1.2 trillion and raised the sock-it-to-me, rate-rising level to $400,000, from $250,000. It agreed — infuriating progressives — to an entirely sensible change in the inflation measurement for calculating tax brackets and cost-of-living adjustments for benefit programs.

The two sides were so close it makes you want to cry, although, in a sign of the trying times, they can’t even agree on how close. On taxes, a mere — yes, mere, given the uncertainties of these projections — $200 billion over 10 years. On spending, the gap depends on whose accounting you buy. The White House says the difference is just $100 billion. Republicans put the number at several hundred billion, but they are suddenly shifting the terms of debate, including about whether lower interest costs should be counted, as they have been, as part of spending cuts.

Either way, these differences are paltry. The rational response would be to keep working to narrow them. But this is Washington, and rationality is fleeting. Just ask John Boehner.