Somewhere, if he’s capable of it, Arthur Finkelstein, the bare-knuckle brawler of a Republican consultant, is smiling.

[IMGCAP(1)]That’s because the “L— word — liberal — is back in vogue, and Republicans once again are poised to bludgeon their Democratic opponents with it.

Embattled Sen. David Vitter (R-La.), still on shaky political ground thanks to his apparent connection to a Washington, D.C., prostitution ring, was the latest to use the tactic. In a Web video last week, he labeled his likely 2010 challenger, Rep. Charlie Melancon (D-La.), a liberal (he accused him of having a “liberal luvfest,— with lobbyists, to be exact).

In Louisiana, embattled becomes emboldened when you can stick the liberal tag on a foe. It’s like the Cold War never ended — Dick Nixon is still calling Helen Gahagan Douglas “the pink lady,— only it’s 2009 instead of 1950.

This must be something of a relief for the GOP, which was largely unable to use the liberal smear in the past two election cycles — at least with any effectiveness — owing to the fact that Republicans had to defend the mess they’d left the country in. Now, with the Democrats fully in power, and the country still a mess, the GOP can and will use the L word to great effect.

The question is, what do Democrats do about it?

From the day he was elected, President Barack Obama and his advisers have been determined about one thing: to avoid the mistakes Bill Clinton made. But as the debate over health care reform reaches its apex — some would say its nadir — Obama seems to have fallen into the very trap Republicans laid for Clinton.

While attempting to walk a centrist path, Obama, like Clinton before him, has unwittingly ceded the center, allowing Republicans to label Democrats as liberals regardless of whether they behave that way.

On health care, Obama quickly dismissed the notion of pushing for a single-payer plan. That was a mistake.

You can argue the policy specifics till you’re blue in the face, and match statistics with statistics when talking about the relative effectiveness of government-run health care in places like Canada, Great Britain and so on. But by taking single payer off the table so quickly, Obama guaranteed that his preference for a health care reform plan, featuring a public insurance option, would sound like the most radical proposal out there.

Small wonder that so many Congressional Democrats are going through gyrations now to distance themselves from the Obama plan — and to find something more palatable to their donors in the health care establishment. Heck, Democrats won’t even point out that Medicare, run by the government from top to bottom, is the most popular health care program out there.

Republicans? All they’ve got to do during the health care debate is repeat at regular intervals their support for reform, watch Democrats tie themselves into knots, shake their heads sadly, and throw the L word around every now and then.

Same with the stimulus package. Obama had to grovel to get a majority of Members to support the $787 billion stimulus, when many economists — then as now — said an even greater infusion of cash was necessary to truly jump-start the economy. So why didn’t Obama, at the very beginning of his presidency, at the very height of his popularity, push harder for more?

Republicans are going to call Democrats liberal no matter what the Democrats do. So why don’t Democrats take their tails out from between their legs and behave like true progressives for once? Stand for something, try to accomplish something, if you’re going to take the heat anyway.

Of course, there are political calculations to be made and pitfalls to consider. Democrats do have several potentially shaky House and Senate incumbents in conservative states and districts. Party leaders understand this — even if the Democratic left does not — and will work hard to defend them and give them leeway on key votes whenever they can.

When the Democrats expanded their Congressional majorities last year, a lot of party activists assumed the chambers would move sharply to the left. It hasn’t happened. Sure, Speaker Nancy Pelosi (D-Calif.) is more liberal than her predecessor, Dennis Hastert (R-Ill.), just as Obama is far more liberal than George W. Bush. And surely freshman Rep. Walt Minnick (D-Idaho) — a veteran of the Nixon administration, incidentally — is more liberal than the man he ousted last year, ex-Rep. Bill Sali (R), though not by much.

But Idaho’s 1st district did not become San Francisco overnight. Minnick will have to vote his district to preserve his Congressional career, and that means taking a lot of votes that Sali would have — and that Rep. Jerrold Nadler (D-N.Y.), say, never would.

It will of course require an enormous amount of compromise to get health care reform passed. The deal probably will be cut in the center, and that’s as it should be.

But politics — and even policymaking — demands a healthy degree of stagecraft. If, as a Democrat, you’re not going to pound the table and raise populist hell every now and then — even if you are going to compromise in the end — what’s the point?

A lot of people thought Bill Clinton was bloodied so badly — and that the Republicans seized control of Congress — in 1994 because his health care plan was too radical and went too far. In truth, Clinton put forward a reform proposal that was such a hodgepodge and attempted to appease so many interests that it actually did very little and collapsed under its own weight.

Would Democratic losses in the House and Senate have been any more devastating than they were in 1994 if Clinton had put forth a principled, streamlined and — yes — radical plan? Probably not. In fact, he might have won some political points for his courage.

Instead, Democrats lost control of the government, Clinton had to remind people that he was relevant and he wound up governing like a moderate Republican for most of the rest of his presidency. It made it that much easier for Bush to push the political pendulum further to the right when he became president, despite the fact that he lost the popular vote and had no real mandate at all.

Obama, who has more progressive instincts than Clinton, had a mandate — maybe not to govern from the left, but to bring significant change to this country. He’s trying, but if he staked out even bolder positions, at least initially, he might actually be able to start to achieve the change he believed in. Sure, Republicans will scream and fling around the L word. But they’re going to do that anyway.