After backing conservative insurgents against Republican senators in the 2010 elections, Sen. Jim DeMint promised Republican Senate leader Mitch McConnell and his GOP colleagues that he would not “recruit or support primary challengers to incumbent Republicans” in 2012.

Now that McConnell has proposed a plan to effectively give President Obama carte blanche to raise the debt limit, it’s time for DeMint to declare that — if the McConnell plan goes through — the deal is off.

The McConnell proposal is not a “contingency plan” — it is a sellout. As put forward by the Republican leader last week, it gives President Obama exactly what he asked for at the start of the negotiations: a “clean” debt limit increase. All Republicans get in exchange are clean hands. In this sense, it is politically brilliant. Congress votes to temporarily surrender its power to approve any increase in the debt ceiling to the president, who can then raise the debt ceiling by $2.5 trillion in three increments. Obama would have to list corresponding cuts in spending that all sides know will never be enacted. And Republicans can vote to disapprove each debt limit increase, knowing full well that they cannot stop it without a veto-proof majority. This allows Republicans to claim to have voted against raising the debt limit, when they really voted to allow it. Obama gets to drive up the debt, and thus drive our economy off a cliff — but with no GOP fingerprints.

This is an insult to conservative voters, who are expected to buy Republican claims that they opposed raising the debt limit when they were in fact co-conspirators in raising it with little or nothing in exchange. Even the “hybrid” plan McConnell and Reid are reportedly discussing would cut spending by about $1 trillion less than it raises the debt limit — an abandonment of the GOP goal to ensure that spending cuts are equal to or greater than any increase in debt authority the president is given.

The McConnell plan is exactly the kind of inside-Washington maneuver that gave rise to the Tea Party movement — and inspired conservative insurgents to challenge establishment Republicans in the last election. Don’t be surprised if DeMint makes clear that any Republican who votes for the McConnell plan could end up facing a well-funded conservative primary challenger backed by his Senate Conservatives Fund. There are signs that DeMint might be leaning toward making just such a declaration.

Last month, DeMint told the Hotline that while he still wasn’t planning to target any of his fellow Republican senators in 2012 that could change if Republicans vote to raise the debt ceiling with nothing in return. “If we have folks who go the wrong way on that, it’s going to be pretty hard for me to sit still,” he said. The day after McConnell unveiled his plan last week, DeMint sent out an urgent e-mail to supporters of the Senate Conservatives Fund declaring the McConnell plan “would effectively give the President the power to increase our nation’s debt at will. I want you to know that I strongly oppose this plan and will do everything I can to defeat it.” Bottom line: Republicans who vote for the McConnell plan should not expect DeMint to sit still in their primaries.

What is the alternative to the McConnell plan if Aug. 2 arrives with no agreement? House Republicans should simply pass a smaller debt-ceiling increase — and attach a larger number of spending cuts that Democrats have agreed to in the course of the debt-limit negotiations. The government does not default. Social Security recipients get their checks. And we begin implementing the spending cuts identified in the negotiations thus far. Critics of this approach point out that Obama has pledged that he will not sign such a stopgap bill. He is bluffing — and Republicans should call him on it. Treasury Secretary Tim Geithner recently warned that failure to raise the debt limit by Aug. 2 would lead to “catastrophic damage” to the American economy. Is Obama really going to allow “catastrophic damage” to the economy? Of course not. Republicans should pass a stopgap bill and then dare the Senate to reject it or the president to veto it. Neither will.

Obama thinks he can play hardball with Republicans by scaring seniors — warning that, to avoid default, the government might not send out Social Security checks to 55 million American seniors after Aug. 2, thanks to the GOP. This is a bluff as well. If House Republicans pass short-term legislation to keep those Social Security checks coming, and Obama vetoes it, who are seniors going blame? The Republicans who passed legislation to keep the money flowing or the president who vetoed that legislation?

The McConnell plan presumes that Obama has Republicans in a corner. He does not. But to prevail in this standoff, Republicans need to reclaim the offensive. Jim DeMint can help put some steel in GOP spines — by making clear the consequences of throwing in the towel.