LOOKING FOR PLAN B…. The Center on Budget and Policy Priorities’ Bob Greenstein, who has as much liberal credibility on budget and tax issues as anyone, doesn’t seem to like the “disturbing negative” provisions of the tax policy deal struck by the White House and congressional Republicans. But he wants to see it pass anyway.

“Congress should approve this package — its rejection will likely lead to a more problematic package that does less for middle- and low-income workers and less for the economy,” Greenstein said yesterday. He added that the agreement includes “surprisingly strong protections for low- and middle-income working families.”

Dean Baker, another very credible, highly respected liberal economist, reached a similar conclusion. Prominent lefty wonks like Lawrence Mishel and John Podesta offered the same assessments yesterday.

The New York Times editorial page said Democrats are “in revolt,” but they should “vote for this deal” anyway.

Without this bargain, income taxes on the middle class would rise. Unemployment insurance for millions of Americans would expire. And many other important tax breaks for low- and middle-income workers — including a 2 percent payroll tax cut and college tuition credits — would not be possible.

If angry Democrats blow up the deal, they will be left vainly groping for something better in a new Congress where they will have far less influence than they have now. The middle class and the unemployed would be seriously hurt.

But let’s say they’re all wrong. Let’s assume, for the sake of conversation, that the liberal economists don’t fully appreciate the larger principles at stake here; their stimulus projections are overly optimistic; and their entire perspective is skewed by weakness, a poor understanding of political tactics, and a Neville Chamberlain-like worldview.

Indeed, let’s also say, just for the sake of conversation, that the liberal policy experts lose the argument and Congress rejects the agreement. Dems decide it’s a bridge too far, so they scuttle the deal and take their chances.

What’s Plan B?

I don’t mean this to sound snarky and this isn’t a rhetorical question; I’m genuinely interested in understanding the back-up strategy. When I posed this question yesterday to some Capitol Hill aides I know, they said they’d recommit to fighting even harder for the original Obama tax plan — permanent breaks for those under $250k, Clinton-era top rates for those above $250k. If/when this week’s compromise goes down, Republicans, they said, would likely cave and accept the Democratic approach. They’d be out of options — it’d be a choice between the Dem plan and higher taxes for everyone. Dems would regain the leverage they lost before the midterms.

And that could work. The plan came seven votes shy of 60 the other day, but when push comes to shove, maybe those seven additional votes would come together, and Dems would win this fight over taxes.

But what then? How would extended unemployment benefits pass for the millions of jobless Americans who need them? What happens to the economic stimulus? What’s the strategy for getting quick approval for an expanded earned-income tax credit and the continuation of a college-tuition tax credit? With almost no time left on the clock, after winning the fight on tax policy, is the plan to simply punt on New START ratification, DADT repeal, the DREAM Act, food safety, and health care for Ground Zero workers, hoping for the best in the next Congress?

I understand very well what opponents on the left want to do to the tax deal, and why. I’m less clear on what happens next.

Update: The estimable David Dayen was gracious enough to prepare a response to my inquiry, and I appreciate it.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.