The days Grover Norquist's sway over Republican Party tax policy — and by default, American tax policy — may be over.

A bill, introduced by Republican Senator Tom Coburn today, proposes to end $6 billion in ethanol tax subsidies. If passed, this would end corporate tax breaks for companies in the ethanol business.

This proposal naturally outraged Grover Norquist. Over the years, he’s obtained signatures from most Congressional Republicans, making them pledge to never raise taxes under any circumstances.

As a guest on The Last Word, Coburn said this tax pledge would not stop government officials from doing the right thing, even under pressure.

“Between now and the next year, as we go to solve this problem, everybody knows there’s going to have to be a compromise on some sort of revenue increases," said Coburn. "Grover’s old news. It doesn’t matter what he says, it doesn’t matter what he wants."

Coburn seemed optimistic, adding "We’re going to fix the country, and some of that is going to be revenue increases, that’s the only way you’re going to build a compromise and get it signed by this president."

Senate Republicans, who had signed the tax pledge, voted against Norquist and for repealing the ethanol tax credit. In total, 34 Republicans voted for the bill, though it ultimately failed 40 to 59.

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Sen. Tom Coburn (file)

Now we’re down to five. Sen. Tom Coburn confirmed today he’s leaving the so-called Gang of Six, a bi-partisan group of U.S. Senators working to solve the hot mess that is America’s deficit.

“We can’t bridge the gulf of where we need to go on mandatory spending,” Corburn said today. “I don’t see that there’s going to be any fruition in continuing them at this time.” He said talks sunk to a “discouraging” low as of late.

Coburn blamed the issue of entitlement reform as the main cause of the breakdown.

He leaves behind two other Republican and three Democratic colleagues. Though, Corburn noted it’s unclear whether remaining members will continue to meet without him.

Grover Norquist, founder and president of Americans for Tax Reform, says Sen. Coburn broke a pledge on taxes. In a MSNBC exclusive, Lawrence talked to Norquist about this public dispute and got his take on how to balance the budget. Hint: it doesn't involve raising taxes.

There's one person standing in the way of Republicans doing the right thing when it comes to taxes, and that's Grover Norquist. He has a virtual lock on GOP tax policy. But, one Republican Senator is finally standing up to machine. Msnbc's Lawrence O'Donnell has more in the Rewrite.