If elections have consequences, so do strategies of opportunism that hitch a ride on popular paranoia. From the day this president was inaugurated, the GOP has fed off the forces that coalesced into the angry astringency of the Tea Party movement.

First the GOP maintained lockstep opposition to the stimulus, despite support from Republican economists. Republicans then proliferated lies about health reform — from the chimera of rationing to the nonexistent death panels. They next stoked the fires by pretending that the legislation to crack down on Wall Street was instead a giveaway to Wall Street.

Shrunken and narrowed, the GOP is increasingly dominated by a far-right rump. Republicans are now riding high on the tide of economic discontent. But they are even less popular than the Democrats—and far less popular than Obama — according to The New York Times/CBS poll.  Republican leaders miscalculated their way into a place where their own influence has waned: They’ll lose seats in 2010 that they could have won, and they’ve imperiled the customary route to their presidential nomination, strengthening Barack Obama’s prospects for re-election.

To exploit this opening, Democrats must draw the line on tax cuts for the wealthy.

The predicted dire day for Democrats in November is now looking a little brighter. Senate Majority Leader Harry Reid was a goner in Nevada against any barely reasonable conservative; but instead of a barely reasonable conservative he faces the Palinesque, press-phobic, Social Security–hating, and nearly incoherent Tea Party product Sharron Angle.

Another Tea Party coup in Colorado has widened the path to re-election for appointed Democratic Sen. Michael Bennett, who will benefit from a gubernatorial contest in which his party’s nominee will trounce two opponents — one extremist, the other extremer. And in Alaska, the repudiation of incumbent Sen. Lisa Murkowski has transformed the Democrat in that race from an impossibility into a bare possibility.

Then came the wacky result that may enable Sen. Mitch McConnell to retain his minority leader title after Nov. 2. The Delaware Senate seat held by Joe Biden for a generation was safe for Rep. Mike Castle until a self-styled fiscal conservative with a history of unpaid loans, income tax liens, and allegations of living off campaign contributions captured the hearts of the unhinged. Christine O’Donnell, said Delaware’s GOP chairman, “could not be elected dogcatcher.”

He’s right — and Republican control of the Senate now requires the GOP to run the table in every contest where there’s a plausible chance to win. For example, the GOP has to elect wrestling maven Linda McMahon in Connecticut and smack down the heavily favored governor of West Virginia, who’s running to replace Robert Byrd.

The Party of No’s Faustian bargain with the Party of Tea has gifted Democrats with the likelihood of holding the Senate — and perhaps the House too, where in district after district Republicans have selected exotic nominees — a rogue’s gallery of the far right.

The danger for Democrats is that they will treat the other side’s missteps as an excuse to retreat from a sharp message. How much more evidence do Democrats need to conclude that they have to draw a dividing line against the Bush tax cuts for the wealthy and do it now? This has the potential to redefine the midterms and either stem or turn the tide. Such a strategy can also let Democrats champion long-term deficit reduction and it can motivate the base, changing the composition of likely voters — which is where the GOP now has the advantage.

The president has articulated the argument; now he must sound it repeatedly across the country. House Speaker Nancy Pelosi, who’s proved to be a remarkable leader in the toughest hours, is pushing her caucus to move. The question is: Will Democrats refuse the helping hand inadvertently offered to them by the Tea people?

Whatever the outcome in this election, the Republicans will pay for their Faustian bargain in the next one. If they squeak in now, the tea baggers will be emboldened. If they fall short, the party establishment will face the bitter complaint that Republicans didn’t go far — or far right — enough. In either case, the historic contours of the Republican presidential process will probably be redrawn.

Normally the GOP nominates by primogeniture — the next person in line. For 2012, the nominee in waiting is Mitt Romney, clearly the strongest Republican choice if the economy continues to be troubled. But no matter how he tries to concoct a difference out of small details, Romney will be scorned for working with Ted Kennedy in passing a health  plan in Massachusetts fundamentally similar to Obama-care. To make amends, Romney has enthusiastically endorsed O’Donnell in Delaware. But the GOP is more backlash than party these days; in Utah last spring stalwart conservative Sen. Robert Bennett was denied a place on the primary ballot merely for daring to join with a Democratic colleague in sponsoring a market-oriented health plan.

Indiana Gov. Mitch Daniels, more and more the establishment’s backup if Romney falters, has committed the mortal sin of sensible fiscal contemplation: “At some stage, we may need a tax increase.” He hopes, he adds, for “a grown-up conversation.” With whom? The delinquents who now populate GOP primaries?

So I suspect that in 2012 primogeniture will not restrain the Republican Party. The nomination of the unqualified Sarah Palin is conceivable; she could be the O’Donnell of the presidential primary season, powered by a constituency that dismisses polls from the likes of The New York Times as a left-wing media conspiracy. The GOP’s 1964 tragedy of Goldwater, who was at least a serious figure, could be repeated in the farce of Palin.

Newt Gingrich is positioning himself as Palin with a brain. Gingrich has now become a font of smears and off-the-rail ideas — from privatizing Social Security to the transparently racist charge that Obama channels the Kenyan anti-colonialism of the father he barely knew. With his pandering to both prejudice and extremism, Gingrich could be the 2012 nominee. He would be unelectable.

So would Mike Huckabee, the former Arkansas governor who’s proposed scrapping the progressive income tax, the sinister idea championed by that great socialist Republican Theodore Roosevelt.

In desperation, Republican strategists are thinking of Mississippi Republican Gov. Haley Barbour, who would also compete with an appeal to the birthers, the resentful, and the backlash base. But Barbour was a legendary D.C. lobbyist for the most powerful vested interests, from tobacco to oil. Perhaps he could run on the slogan: “Remove the Middleman.”

For Republicans, payback could come as early as November, with Democrats keeping the Senate — maybe even the House. But 2012, I believe, will provide the ultimate irony: The people who most revile President Obama — and the Republican leaders who enlisted them only to see their party hijacked by them — may assure an Obama re-election.

Told that someone was “his own worst enemy,” Winston Churchill once replied: “Not while I’m alive.” The Tea Party has assumed that status for the GOP.