We keep hearing that the Buffett Rule is “gimmickry.” Well, speaking of gimmickry...

One of the most important things to emerge from Mitt Romney’s overheard remarks at the Florida fundraiser is he finally shared a few specifics as to how he would pay for the massive tax cuts he’d impose as president.

Romney has said that his plan to cut taxes by 20 percent across the board will be revenue neutral — that the tax cuts would be paid for through a combination of eliminating loopholes and deductions, combined with new revenues generated by economic growth. But he hasn’t publicly said which loopholes or deductions he’d eliminate to do this.

At the fundraiser, Romney opened up to his donors a bit on this score:

“I’m going to probably eliminate for high income people the second home mortgage deduction,” Romney said, adding that he would also likely eliminate deductions for state income and property taxes as well.

Okay, so how much of the cost of Romney’s tax cuts would be covered by the elimination of these deductions?

Only one-tenth, according to a tax expert I spoke to today.

The nonpartisan Tax Policy Center has estimated that Romney’s tax cuts would cost $480 billion in revenue in 2015, relative to current policy, and could even grow in the years after that. The Tax Policy Center’s Roberton Williams tells me that by his estimate, the measures Romney identified in his chat with donors would save between $45 billion and $50 billion in 2015.

That still leaves more than $400 billion per year in unpaid-for tax cuts, Williams says.

Of course, Romney would presumably close other loopholes and eliminate other deductions, too. And again, his campaign has insisted that the revenues generated by economic growth will also help cover the cost of the tax cuts. But without specificity, it’s impossible to judge his plan, and the dedutions he has specified would barely put a dent in its cost.

“What Romney has done so far is promised all the desert and said nothing about the broccoli or cauliflower,” Williams says. “He promised all the tax cuts he’s going to do. But he hasn’t said anything at all about the pain side — how you’re going to pay for it. That’s the hard part. Until he spells this out, we can’t really say whether he has a viable plan.”