WASHINGTON (AP) — Under relentless pressure from their right wing, Republicans are in the midst of a risky fight with President Barack Obama they know they will lose, little more than a year before an election that history says they should win.

To minimize the damage, the party must re-define victory as something less than a full defunding of the three-year-old health care law, yet persuade the most conservative GOP supporters that Republican lawmakers succumbed after a principled fight. All without triggering a government shutdown or a default by the Treasury, or otherwise offending independents whose ballots will settle the 2014 elections.

Already, party leaders are making that effort. "I just don't happen to think filibustering a bill that defunds Obamacare is the best route to defunding Obamacare," Sen. Mitch McConnell said archly Tuesday. "All it does is shut down the government and keep Obamacare funded."

That was one day after rejecting the path outlined by the party's rebel-in-chief, Texas Sen. Ted Cruz — who began a speaking marathon on the Senate floor Tuesday afternoon.

Seeking to turn the heat on to Democrats, he said that four years ago they voted for the health care law with the "excuse that they didn't know how it would turn out. Well, they don't have that excuse now. I think we deserve to know where they stand now."

In addition to the future of health care and a possible government shutdown, the perennial struggle for raw political power is at the root of the struggle.

Republicans will need to pick up six seats in 2014 to win control of the Senate, a tall hurdle but not impossibly so. The party out of power in the White House historically has won an average of three to four seats in midterm elections since 1934, and Democrats are defending a half-dozen in difficult circumstances.

In the House, the GOP holds a 233-200 majority with two vacancies, and the historical trends show a 27-seat gain in midterm elections for the party locked out of the White House.

Enter the campaign to defund Obama's health care overhaul, accompanied by the risk of a shutdown or default.

Democrats, holding a Senate majority and seeking the same in the House, figure that chaos is their friend in the current political climate. They calculate that the public will blame Republicans for any interruption in government services or benefits, as it did two decades ago in the last shutdown confrontation that approximates the current one.

As a result, Democratic leaders employ rhetoric designed to raise questions about the mental health of some members of the Republican rank and file, if not their intelligence. Majority Leader Harry Reid of Nevada routinely refers to them as tea party "anarchists." Sen. Chuck Schumer if New York says they have embarked on an "insane plan." New York Rep. Steve Israel, who heads the House Democratic campaign committee, says Republicans have launched a "kamikaze mission to shut down the U.S. government and our economy."

Speaking over the weekend to the Congressional Black Caucus Foundation, Obama was less personal but just as pointed.

"This is an interesting thing to ponder, that your top agenda is making sure 20 million people don't have health insurance," and you are willing to shut down the government to win the point, he said.

Behind the president's remarks lie Democratic assumptions that the health care law isn't as unpopular as Republicans say it is, and that millions who now lack coverage will decide they like it once they have it.

In a three-cornered fight, each side cites polls to prove its point.

Cruz and his allies are focused largely on the tea party slice of the electorate as they flirt with a partial shutdown — an outcome the Texan says he doesn't want — in their drive to defund "Obamacare." McConnell and other Republican leaders focus on other soundings. So do Obama and congressional Democrats.

Each finds something to like in a survey by the Pew Research Center.

Among the general population, just 33 percent of those surveyed said they want lawmakers to defund Obamacare if it means a government shutdown.

For independents, it is 36 percent, sobering for Republicans whose goal is to win a majority in November, rather than merely a series of primaries.

Among tea party members, 77 percent said they want to defund Obamacare even if a shutdown results.

That's enough to give hope to a challenger running against even the most entrenched Republican next fall, and to a potential 2016 GOP presidential candidate as well.

After eight months in the Senate, Cruz is already counted among them, and he has easily eclipsed fellow White House hopefuls Rand Paul and Marco Rubio as the face of the drive to "Defund Obamacare."

The Texas Republican co-stars with fellow Sen. Mike Lee of Utah in television commercials to promote the cause. The ads are funded by the Senate Conservatives Fund, one of a cluster of organizations that makes a specialty of backing tea party-aligned challengers in congressional primaries.

For now, at least, establishment Republicans speak dismissively of such organizations, which they accuse of seeking to raise money for their own political purposes with little or no concern for the broader fortunes of the party. Yet they can scarcely ignore them.

In its latest filing with the Federal Election Commission, the SCF reported receiving contributions of $1.5 million in August, roughly as much as the previous four months combined.

Nor is there much mystery about how it intends to spend some of it.

It has already aired ads targeting McConnell. He "is the Senate Republican leader but he refuses to lead on defunding Obamacare," said one commercial that aired in Kentucky and was backed by more than $300,000. The group seems to be moving steadily toward endorsing Matt Bevin, who is challenging McConnell for the Republican nomination to the Senate next year.

Some tea party-backed challengers, including Cruz, Paul and Rubio, have won Senate seats in recent years after defeating incumbents or establishment-backed candidates. But the list of those who won nominations only to lose elections that were clearly winnable is longer, in Nevada, Colorado, Delaware, Missouri, Indiana.

Long enough to have cost Republicans chances at winning the majority in 2010 and 2012, and threaten any chance they have in 2014 as well.