With tea party-, Sarah Palin- and Jim DeMint-backed candidates winning Republican primaries all over the country, it’s hard not to conclude that the GOP is committing suicide.

[IMGCAP(1)]Or, as one GOP insider put it Wednesday, “we’re going to hell in a tea caddy.”

In the short term, victories by former fringe candidates Christine O’Donnell in Delaware and Sharron Angle in Nevada diminish — but do not eliminate — GOP chances of taking control of the Senate in November.

But, worse, the growing strength of right-wing ideologues threatens to shove the GOP into territory occupied by Democrats: out of the mainstream of U.S. opinion.

And, even worse than that, a harder-right GOP contingent in the House and Senate — whether in the majority or not — will make it harder to solve any of America’s huge problems, which will require compromise with President Barack Obama.

Right now, the “establishment” Republicans leading the GOP in Congress near-automatically oppose every important Obama initiative.

With hard-liners such as Joe Miller (Alaska), Mike Lee (Utah), Ken Buck (Colo.), Marco Rubio (Fla.), Rand Paul (Ky.) and former Rep. Pat Toomey (Pa.) bolstering right-wing ranks led by Sen. Jim DeMint (S.C.), agreement on taxes, budgets, entitlement and immigration reform — even education reform — may well become impossible.

It’s even conceivable that Republicans could repeat the disastrous 1995 stunt of shutting down the government — perhaps this time over health care funding — which helped President Bill Clinton recover politically and win re-election in 1996.

The perpetrator of that faux pas, then-Speaker Newt Gingrich (R-Ga.), shows every sign of being so caught up in the right-wing ascendancy that he’s gone extremist in his bid to be the 2012 GOP presidential nominee.

To top off calling Supreme Court nominee (now Justice) Sonia Sotomayor a racist, likening Islam to Naziism and raising the specter of a “secular-socialist” takeover of America, Gingrich has endorsed the idea that Obama is, at bottom, a Kenyan anti-colonialist who hates western culture.

Among other GOP presidential candidates, Minnesota Gov. Tim Pawlenty is already repeating Mitt Romney’s 2008 mistake of going nativist to appeal to the right.

To be sure, not all tea-party-backed candidates are so “out there,” but Rush Limbaugh-inspired vilification of Obama is running deep in the party.

Calling him “alien” is now respectable, and the just-nominated GOP candidate for New York governor has distributed e-mails depicting Obama and the first lady as a pimp and prostitute.

Warning to the GOP: While the latest Quinnipiac University poll shows that Obama’s approval rating is 44 percent, an all-time low, 55 percent regard him as “honest and trustworthy” and 59 percent say he has “strong leadership qualities.”

Obama’s “favorable” rating is down to 47 percent, but Palin’s is 31 percent and the tea party’s is 30 percent. Only 12 percent of Americans say they belong to the movement.

Approval of the Democratic Party’s performance in Congress is down to 30 percent — 19 percent among independent voters.

But approval of Republicans in Congress is 29 percent overall and 23 percent among independents.

Democrats have sunk so low since 2006 and 2008 because they have gone too far left, proposing big-government solutions to every problem and swelling the national debt.

A Gallup poll in June showed that 49 percent of voters thought the Democratic Party “too liberal,” while 38 percent thought it “just right.” Forty percent thought the GOP “too conservative” and 41 percent “just right.”

What’s going to happen when it sinks in with the public that Republicans want to make all of President George W. Bush’s tax cuts permanent, adding $3.9 trillion to the national debt? It may not hurt them in this election, but eventually, it will.

Of course, as Democrats lose marginal seats, their ranks will become more solidly liberal. That won’t matter much if they lose control of the House, but it will further polarize American politics.

Two very bright conservatives, New York Times columnist David Brooks and Peter Berkowitz of Stanford University’s Hoover Institution, have warned recently that conservatives need to remember that, if elected, they have a responsibility to govern and solve problems, not just oppose government.

“Those responsibilities,” Berkowitz wrote in the Wall Street Journal, “include putting people to work and reigniting the economy — and devising alternatives to Obamacare … to provide affordable and decent health care.”

As Brooks wrote this week, “if the current Republican Party regards every new bit of government action as a step on the road to serfdom, then the party will be taking [the] long, mainstream tradition [of government action dating to George Washington and Abraham Lincoln] and exiling it from the GOP.”

The GOP is heading out of the mainstream. The disastrous examples of Barry Goldwater in 1964 and George McGovern in 1972 should be instructive.