The effort by conservatives in the House and Senate to threaten a government shutdown over Obamacare could force Speaker John A. Boehner into the arms of House Democrats.

With 60 Republicans already pushing the Ohio Republican to defund Obamacare in any spending bill, the speaker may not be able to cobble together a House majority on a bill that President Barack Obama would sign without Democratic votes. And he’s not likely to get those votes for free.

A dozen Republican senators led by Mike Lee, R-Utah, already signed a letter vowing to vote against any continuing resolution that funds Obamacare. And Rep. Marlin Stutzman of Indiana — who helped torpedo GOP leaders’ first attempt at a farm bill — became the first House Republican last week to make the same absolutist pledge.

“I’m not going to vote for a continuing resolution that funds Obamacare,” Stutzman said in a July 25 release. “It makes no sense to spend another dime on a failed law that the president has already delayed.”

But senior aides from both sides of the aisle say the threat would surely backfire on Republicans if they carry it out. For one thing, most of Obama’s new health care program is mandatory spending that is not affected by appropriations bills, so it would continue to receive funding in any event.

“Even if you shut down the government, Obamacare will continue to be funded, and all you will have accomplished in that scenario is a government shutdown,” a senior Republican appropriations aide said.

Such thinking generally tracks with comments made last week by several prominent Republicans, including Rep. Tom Cole and Sen. Tom Coburn of Oklahoma and Sen. Richard M. Burr of North Carolina, among others.

They have variously warned that Obama will never sign a law defunding his administration’s signature piece of legislation, that Boehner will have to go to Democrats — hat in hand — to pass a CR if he can’t find the votes in his own conference and that a shutdown would be blamed on Republicans and cost them dearly politically.

Cole told MSNBC on Monday that a defunding- sparked shutdown was a “suicidal political tactic.” Burr, a close friend of Boehner’s, called it the “dumbest idea I’ve ever heard of,” while Coburn told the Washington Examiner’s Byron York that it would be “a good way for Republicans to lose the House.”

Democrats believe the defunding fight will paint the GOP as extreme.

Drew Hammill, the communications director for Minority Leader Nancy Pelosi, D-Calif., said “no one has talked about a shutdown except for them.

“Obviously it falls into part of a narrative: just lurching from manufactured crisis to manufactured crisis,” Hammill said. “It’s almost like clockwork.”

Aides note that the shutdown talk steps on the GOP leadership’s current messaging strategy, which has been focused on accusing the White House and Democrats as the ones threatening a shutdown so they can spend more.

In the meantime, the fight represents another bruising skirmish in the ongoing GOP civil war between leaders and insurgent conservatives backed by the Club for Growth, Heritage Action for America and a number of conservative talk show hosts who are fanning the shutdown flames.

If past is prologue, the trio of Boehner, the White House and Senate Democrats will find a way to muddle along and avert a shutdown.

The question for Boehner is whether he will initially include an Obamacare defunding rider as a sop to conservatives to get a bill to the Senate — knowing full well that the Senate would then amend the bill, stripping the Obamacare rider and perhaps adding more spending to boot.

Alternatively, Boehner would have to cut a deal with Democrats initially. Many Republicans want to keep the stopgap bill to $967 billion — the level prescribed by the 2011 Budget Control Act after sequester. But House Republican appropriators are eyeing a short-term bill aimed $21 billion higher, or $988 billion, the same level as this year and a number more likely to attract Democratic votes.

Democrats and the White House, meanwhile, still haven’t decided how much hardball they want to play.

While White House spokesman Josh Earnest on Monday said the White House doesn’t want a shutdown, he didn’t clarify what the president would sign. So far the White House has threatened to veto every House spending bill absent a larger budget agreement, and Senate Majority Leader Harry Reid, D-Nev., said last week he would do whatever he could to oppose a CR at the $967 billion sequester level.

The House Republican appropriations aide warned that defunding Obamacare through the CR would simply end negotiations. The aide said the “real negotiation, however, is not on a CR, but will and should be on a larger deal over undoing sequestration.”

The aide continued that a “clean, short-term, no-drama CR at current levels” should have Democratic support already; the only haggling point would be how long you keep the government funded so that appropriators from both chambers could finish their work.

But more than 60 House Republicans, led by North Carolina Republican Mark Meadows, called on Boehner and Majority Leader Eric Cantor, R-Va., to defund Obamacare “in any relevant appropriations bill brought to the House floor in the 113th Congress, including any continuing appropriations bill.”

However, as Ryan Ellis — the tax policy director of Grover Norquist’s Americans for Tax Reform — points out, “distinctions matter here.”

Ellis told CQ Roll Call on Monday that while Americans for Tax Reform is against the ultimatum letter sent by Lee and others, ATR would “cheerfully support” the House letter.

“There are many conservatives who would say they want to have a vote on Obamacare defunding in a CR, but who have not said they will vote against any CR which lacks such defunding,” Ellis said. “Those are two very different things.”

As Ellis noted, at some point, you have to cut a deal. Chip Roy, chief of staff to Sen. Ted Cruz, R-Texas, a signer of the Senate ultimatum letter, blasted opponents of the shutdown strategy with the hashtag #surrendercaucus on Twitter.

Ellis took him to task.

“The problem with the Lee letter is that it leaves us no room to do the eventual negotiation we know we have to do,” he tweeted back.