Mitt Romney, you got some ‘splainin’ to do!

That was the gist of President’s Obama’s broadside against Paul Ryan’s budget in a scorching address Tuesday in which the president dubbed the GOP plan the kind of “radical” “social Darwinism” that’s an affront to American values. He also noted conveniently for the assembled press that Mitt Romney has called Ryan’s plan “marvelous.”

A word, the president added slyly, in a nod to Romney’s infamous common touch, that you not only don’t hear applied to budgets often, but that you also don’t hear often, period.

Ordinarily, one would say it’s hard to imagine the West Wing’s glee when Ryan got his troops to walk the plank again and pass a fresh version of last year’s extreme, regressive blueprint. But, in fact, I can imagine it perfectly.

I worked with many on the president’s senior team back when they were in the Clinton White House in the ’90s. So I can conjure up the frisson of excitement Obama economic adviser Gene Sperling felt when Ryan’s plan was unveiled, and then once more when the House passed it. The idea that Republicans were sticking their heads in the noose again had to seem like an unbelievable stroke of political luck. Luck that was only compounded by Mitt Romney’s full-throated endorsement of Ryan’s plan on the campaign trail.

I can see Sperling calling in minions to prepare the killer analysis in Obama’s speech Tuesday that would pound home what is sure to be a Democratic mantra this year: all the things that could be bought with the $150,000 average annual tax cut that top American earners stand to get if Romney and Ryan have their way.

It’s a pretty stunning list: “A year’s worth of prescription drug coverage for a senior citizen. Plus a new school computer lab. Plus a year of medical care for a returning veteran. Plus a medical research grant for a chronic disease. Plus a year’s salary for a firefighter or police officer. Plus a tax credit to make a year of college more affordable. Plus a year’s worth of financial aid.”

Not to mention the phoniness of the GOP’s concern with debt and deficits, when the choices above reveal the party’s true priorities.

I can see the focus group of independent voters reacting with shock and revulsion when they heard these comparisons. The thumbs-ups of David Axelrod and David Plouffe behind the two-way mirror as they texted White House speechwriters, “It’s a go.”

What was unveiled with Obama’s powerful speech is nothing less than a replay of Bill Clinton’s reelection argument in 1996. Back then, a colorless GOP leader named Bob Dole was successfully lashed to revolutionary Newt Gingrich’s budget, which Democrats argued would ravage Medicare, Medicaid, education and the environment. Dole was morphed into Gingrich at least 125,000 times in negative ads (according to Gingrich’s later tally for me), killing Dole with independents and sullying Gingrich’s brand forever.

Now Romney, who will start this fight with the highest negatives (over 50%) of any general-election contender in memory, confronts a political play that the president’s men invented and have been honing for 15 years.

None of this changes the fact that the election will be close. It starts at roughly 45-45, with just a small slice of the electorate up for grabs. Those swing voters will almost certainly find Obama’s Romney-Ryan case compelling.

Can Romney extricate himself from being tied to Ryan as Dole was to Gingrich? This kind of Houdini-style escape may be beyond even the skills of as brazen a flip-flopper as Romney, though it will be fun to watch him try.

After all, if the man who was for the health-care mandate before he was against it turns out also to have been for the Ryan budget before he was against that, he’ll alienate his base in an attempt to woo the middle. Meanwhile, Romney’s support for Ryan will run in endless loops in the president’s and his super PAC’s ads, along with a devastating catalog of all of Romney’s other switcheroos over the years.

The question is whether a sluggish economy and still-high unemployment can trump the vise Romney has stuck his head in by supporting Ryan. If no external shock intrudes — Europe’s debt crisis comes roaring back or Israel strikes Iran, for example — I’d bet not.

Does any of this mean an Obama returned to office on these terms can make substantive progress in a second term? Perhaps. Clinton was poised to do big Nixon-to-China entitlement reforms with the GOP until the Lewinsky mess exploded. Obama, one assumes, won’t be facing such land mines.

To be sure, the campaign will be ugly, and partisan feelings more bitter than ever by the end. But if one were inclined to hope, one would say that calling out and beating back the crazy rightward lurch of the modern GOP, as Obama has now decisively begun to do, may well be a prerequisite to some genuine problem-solving after November.

Matt Miller, a co-host of public radio’s “Left, Right & Center,” writes a weekly online column for The Post. His e-mail address is mattino2@gmail.com.