What if he wins? ... Mitt Romney, that is.

The emergence of the new, improved model, “the Moderate Mitt,” as the media have dubbed him, has Democrats in a sputtering rage. How dare he abandon his hard-won image as idol of the idiot right!

It’s a reaction that’s more than a little astonishing. One would think a party of chest-beating liberals would welcome a Republican who has, overnight, been reborn as — abracadabra! — a defender of Medicare and middle-class tax cuts, advocate of Wall Street regulation and women’s rights, and one who’d never, never, ever cut taxes for the rich. Perish the thought.

That’s the Mitt who emerged from his debate with President Obama. It was a makeover for the record books.

The new Romney, if that’s what we’ve got here, is good for his own election chances, for a return to sanity for the Republican Party and — if he’s for real — good for the country itself, should he be elected.

But what about all that nasty stuff to the contrary he’s been spouting for a year? Ay, there’s the rub. Which Romney would be the one taking the oath of office?

Romney may not be the most predictable and consistent presidential candidate, but he’s the most interesting. Why? Because if he wins the White House, he will very likely carry enough Republicans with him to give the GOP control of the Senate as well as the House. In short, the end of divided federal government — at least for the moment.

Republicans would enjoy total control in Washington, with only the threat of a filibuster by a Senate Democratic minority as a restraint on their power.

Would they rule as a muscled-up extension of the tea party on steroids, with its mindless hostility to the federal government, and run the government into the ditch again as Republicans did in the George W. Bush years? (Forgot that, did you?)

Or would they follow a President Romney, now free of the need to butter up the rabid right, on a more moderate course calculated to attract Democratic support and begin an end to the destructive partisan divided in D.C.?

The answer would depend on Romney himself — what he truly believes and how he’d use his leverage with Congress and the country.

As a new president, the one who’d deposed an Obama hated by the hard right, Romney would take office with the heartfelt gratitude of the GOP, both its old guard of corporate kingpins and the party’s firebrand foot soldiers, the tea party and its true believers. He’d own their loyalty — at least for a time — and odds are they’d follow his lead, even into the quicksand of compromise on touchy social issues.

There should be little doubt about Romney’s ability as a manager; that’s where he made his reputation. But he’s not nearly so sure-footed as a politician. And it’s as a politician that he’d have to weigh how strong a hold he has on his party in Congress and how far he could push it on issues of his choice.

All of which makes the question of what policies he’d push critical. Other than his commitment to cutting taxes and hiking defense spending, we don’t know what policies he’d pursue or even what programs and tax loopholes he’d cut to pay for tax reductions and a big defense spending increase. He won’t say.

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On that score, he’s running a kind of stealth candidacy that troubles even some Republicans.

Last week, for example, he told the Des Moines Register, “There’s no legislation with regard to abortion ... that would become part of my agenda.” Within hours, GOP conservatives who want to ban abortion blew a gasket, forcing the Romney team to rush out a reassuring statement that “Gov. Romney would, of course, support legislation aimed at providing greater protection for life.” A little something for everybody?

With his penchant for secrecy and dread of detail, Romney is a political puzzlement, a candidate asking Americans for a blank check on most issues.

In all likelihood, he has strongly held beliefs. But maybe he doesn’t. There’s even the chance he hasn’t yet decided where he stands on the big issues, that he’s still a work in progress.

It’s what makes him clearly the most interesting presidential candidate, but also the least predictable or reassuring.

John Farmer is a Star-Ledger columnist. His column appears Sundays.

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