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Republicans are seriously considering a Doomsday Plan if fiscal cliff talks collapse entirely. It's quite simple: House Republicans would allow a vote on extending the Bush middle class tax cuts (the bill passed in August by the Senate) and offer the President nothing more: no extension of the debt ceiling, nothing on unemployment, nothing on closing loopholes. Congress would recess for the holidays and the president would face a big battle early in the year over the debt ceiling.

Two senior Republican elected officials tell me this doomsday plan is becoming the most likely scenario. A top GOP House leadership aide confirms the plan is under consideration, but says Speaker Boehner has made no decision on whether to pursue it.

Under one variation of this Doomsday Plan, House Republicans would allow a vote on extending only the middle class tax cuts and Republicans, to express disapproval at the failure to extend all tax cuts, would vote "present" on the bill, allowing it to pass entirely on Democratic votes.

Infographic: The Fiscal Cliff

By doing this, Republicans avoid taking blame for tax increases on 98 percent of income tax payers. As one senior Republican in Congress told me, "You don't take a hostage you aren't willing to shoot." Republicans aren't willing to kill the middle class tax cuts, even if extending them alone will make it harder to later extend tax cuts on the wealthy.

Rep. Tom Cole, R-Okla., an influential conservative House Republican, is already on record supporting extending the middle class tax cuts - with or without the upper income tax cuts. On Sunday, he said Republicans should embrace the extension of the middle class tax cuts and take credit for it.

"That's a victory, not a loss," Cole said on This Week with George Stephanopoulos. "And then we're still free to try and fight over higher rates, offering revenue, which the Speaker has put on the table."

Last week, Boehner said he disagreed with Cole. But now a version of what Cole has called for looks more and more likely to happen.

Still unclear under this plan is what would happen to the automatic defense cuts - " sequestration" - scheduled to go into effect on January 1 without a deficit deal. During the campaign, the President promised the cuts would not happen. As part of the deal to allow the House vote on taxes, those automatic defense cuts could be put off for a year.

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