John Boehner began the post-election public negotiations on the fiscal slope by proposing Mitt Romney’s tax plan of lower rates and a broadened tax base through limits or eliminations of deductions. But he’s not the only person in Washington eyeing the Romney plan. Democrats have an appetite for one part of it as well.

With both parties positioning for difficult negotiations to avert a fiscal crisis as Congress returns for its lame-duck session, Democrats are latching on to an idea floated by Mitt Romney to raise taxes on the rich through a hard cap on income tax deductions.

The cap — never fully detailed by Mr. Romney — is similar to a longstanding proposal by Mr. Obama to limit income tax deductions to 28 percent, even for affluent households that pay a 35 percent rate. But a firm cap of around $35,000 would hit the affluent even harder than Mr. Obama’s proposal, which has previously gotten nowhere in Congress.

“Let’s just say there’s a renewed interest,” said Senator Kent Conrad, Democrat of North Dakota and chairman of the Senate Budget Committee. “Part of it is people reflecting on Obama’s proposal, but when Romney said what he said, it just added fuel.”

I’ll just butt in at this point to note that Mitt Romney lost the election. And the election was predicated on higher taxes on the wealthy. A deduction cap could potentially lead to higher effective taxes on that part of the population, but Romney always envisioned it, as does Boehner, as a way to accmmodate LOWER rates.

There could be a good reason to cap deductions; I thought it was a good idea when President Obama proposed it back in 2009. I should note that it went nowhere at all, and that this came at a time when Democrats had wide majorities in Congress. To do it in service of lower rates would be a total scandal.

And let’s be clear about who a deduction cap would hit the hardest. Those individuals with the highest deductions are typically the ones who live in areas with high housing prices, who benefit from the mortgage interest deduction and other high cost-of-living liabilities that can potentially get written off. In other words, rich coastal liberals – Obama’s fundraising base – would pay the price for much of a policy change like this. Not a reason not to do it, but truly a giant middle finger propped up directly at those who made the second term happen.

Congressional Democrats, so far, are saying that the deduction cap would not be a substitute for higher tax rates. In fact, the Bowles-Simpson recommendations assumed the higher rates on the wealthy before instituting its base-broadening, revenue-generating program. President Obama, by contrast, has said nothing this specific. Presumably he will get pressed on the matter at a press conference tomorrow.