The Republican Party’s annus became considerably more horribilis this week, with Arlen Specter switching parties, President Obama taking what amounted to a 100-days victory lap (despite the economy’s continuing decline), and a new poll showing that even the GOP’s most reliable wedge issues (gay marriage and immigration) have largely lost their traction with swing voters. Even poor Susan Collins, the moderate senator from Maine who got flu-pandemic-preparedness funding stripped from the stimulus bill for entirely principled reasons, appears short-sighted and Scrooge-like (in other words, like a mainstream Republican) as the Swine Flu scourge grows.

Specter’s big switch has opened yet another gaping wound in the party, as its few remaining sane people moderates bemoan the ugly extremism (would you like some tea and assault weapons to go with those accusations of fascism?) that has driven the number of self-identifying Republican voters to an abysmal 21 percent of the electorate. Meanwhile, Rush, Newt, Kristol and the rest of the GOP booboisie are actually celebrating “Benedict Arlen’s” departure as one more step toward ideological purity, even as the influence of elected Republicans upon national policymaking has faded from “just a little” to “practically none” – or, perhaps, “exactly as much as Obama is willing to give them as he continues to pay lip service to bipartisanship.”

Arlen SpecterStill, any political analyst with, say, 15 years of hindsight will tell you that “Specter the Defector’s” move across the aisle (he’s done this before, having become a Republican to run against his boss for Philadelphia district attorney in 1965) is just as likely to haunt Democrats as they approach next year’s midterm elections. It was perhaps the perfect political calculation — You want a filibuster-proof majority? Well, I want to save my electoral ass! – but Specter’s presence in the Democratic caucus probably won’t engender a profound shift in his political beliefs. He says he’s still against the Employee Free Choice Act (i.e., card-check unionization votes), though he’s already flip-flopped on the issue once – he voted for it last year, then announced his opposition as Pennsylvania right-wingers held an AK-47 to his head. He’s opposing Obama’s appointee as legal counsel in the Justice Department. Just last night, he voted against Obama’s 2010 budget proposal because he doesn’t like the rules it establishes for debating health-care reform in the fall.

Yes, Democrats will have a 60-vote majority as soon as Norm Coleman gives up the ghost and Al Franken is seated as Minnesota’s new senator. But that doesn’t mean they’ll march in lockstep behind Obama’s programs, or that they’ll jump whenever Harry Reid cracks the whip. (Republicans do lockstep far better than Democrats – their 55-vote majority in 2005-06 was probably stronger than this Democratic majority will prove to be.) At least since the Vietnam War and the 1968 convention shattered the New Deal coalition, Democrats have bungled every attempt to march in formation. They blew it during the Carter administration despite huge post-Watergate congressional majorities, as the executive and legislative branches became at times openly hostile toward one another. They blew it again in 1993-94, when Sam Nunn’s defiance on gays in the military dealt Bill Clinton an early blow (sorry) and senators’ cowardice in the face of insurance-industry lobbying killed health-care reform. (The myth of the 1994 midterms is that populist anger at the Democrats’ big-government plans brought about the “Republican Revolution”; the truth is that it was the Democrats’ incompetence and scandals that brought them down, just the way similar foibles laid the GOP low in 2006.)

The Democrats’ lack of discipline is legendary, but it’s understandable; ever since FDR forged that New Deal coalition, the party has been exactly that – a loose affiliation of interests working toward common goals, a “big tent” in the way the Republicans never truly were even when Ronald Reagan claimed it to be so. Today, their Senate caucus includes Michigan’s Carl Levin (a perpetual roadblock to increased fuel-efficiency standards in automobiles), Nebraska’s Ben Nelson (who represents a red state and is too attached to ethanol), North Dakota’s Kent Conrad (who will forever hold his party hostage to farm subsidies) … and now Specter, whose position on every issue seems calculated to maximize his personal political benefit while driving his colleagues up the wall.

With his addition, the Democrats have just enough of a numerical advantage to be dangerous – to themselves. With 60 potential votes in their own caucus, they will be negotiating energy, health care reform, education and entitlements largely amongst themselves, with little Republican input necessary – until one of their moderates becomes intractable, at which point they’ll have to go back to the well with Collins and Olympia Snowe, as they did on the stimulus.

Meanwhile, the remaining Republicans will be crowing over every detail the Dems can’t nail down. And if any of the major items on Obama’s agenda should actually fail, the Democrats will have no one to blame but themselves. Every struggle will be magnified, and with the economy likely to remain in the toilet for the next year or two, they’ll be much more likely to pay for any failures in November 2010.

Al FrankenThe truth is, Democrats might have been in much better shape had Specter stayed put. With only 59 senators – and #59 coming in the form of Franken, who, let’s face it, is hardly likely to make a Kennedyesque impact on the chamber – the Dems could have gone into 2010 blaming Republican recalcitrance for any bills that died in the face of filibuster. With the electoral calculus in their favor – more GOP seats are expected to be seriously contested next year – the Democrats might have emerged with a 63- to 65-seat majority, negating the moderates’ potential apostasy.

That still might happen anyway, particularly if Obama continues to be held in the same high regard he is today, but it will be considerably more difficult. Of course, even a dyed-in-the-wool liberal should recognize that unchecked one-party governance is dangerous, so it’s hard to grumble too much about moderate push-back within the Democratic Party. Still, reversing the economic downturn (and undoing the disasters of the last eight years) will require the sort of Herculean strength of will that one-party governance (at least for a while) can provide – if that one party can keep its ducks in a row.

As Uncle Ben always said, with great power comes great responsibility. Democrats now have the power; the trouble is, they’ve never been all that good at the responsibility part. Now they get to prove themselves again, with no good excuses for failure, and the nation will be watching closely to see if they can pull it together rather than implode. I wouldn’t put money on either outcome.