In Washington's coming budget battles, sacred cows like the tax deductions for home mortgage interest and charitable donations are likely to be on the table along with potential cuts to Social Security and Medicare.

But no one on Capitol Hill believes Wall Street's beloved carried-interest tax loophole will be touched.

Don't blame the newly elected Republican Congress.

Democrats didn't repeal the loophole when they ran both houses of Congress from January 2009 to January 2011. And the reason they didn't has a direct bearing on the future of the party.

First, let me explain why this loophole is the most flagrant of all giveaways to the super-rich.

Carried interest allows hedge-fund and private-equity managers, as well as many venture capitalists and partners in real estate investment trusts, to treat their take of the profits as capital gains — taxed at maximum rate of 23.8 percent instead of the 39.6 percent maximum applied to ordinary income.

It's a pure scam. They get the tax break even though they invest other peoples' money rather than risk their own.

The loophole has no economic justification. As one private-equity manager told me recently, “I can't defend it. No one can.”

It's worth about $11 billion a year — more than enough to extend unemployment benefits to every one of America's nearly 3 million long-term unemployed.

The hedge-fund, private-equity, and other fund managers who receive this $11 billion are some of the richest people in America. Forbes lists 46 billionaires who have derived most of their wealth from managing hedge funds. Mitt Romney used the carried-interest loophole to help limit his effective tax rate in 2011 to 13.9 percent.

So why didn't Democrats close it when they ran Congress?

Actually, in 2010 House Democrats finally squeaked through a tax plan that did close the carried-interest loophole, but the Democratically-controlled Senate wouldn't go along.