If the Democrats somehow contrive to blow this presidential election, they should be consigned to the dustbin of history - or to a display case at the Smithsonian, where perhaps they can share space with the Whigs.

Seriously, think about it. The economy is tanking, yet their autumn opponent, John McCain is on record saying, "The issue of economics is not something I've understood as well as I should." The Iraq war continues to kill our kids and bleed us to the tune of $3 billion a week, yet McCain, who sometimes confuses the Sunnis with the Shiites, remains its unapologetic cheerleader. Meanwhile, nearly 80 percent of the American people think the country is on the wrong track - a legacy of the current Republican president, who now has the highest disapproval rating (69 percent) in the history of the Gallup poll.

Yet, McCain is deadlocked in the polls with his two Democratic rivals. He is traipsing around the nation on his "Time for Action Tour," blissfully unscathed and husbanding his septuagenarian strengths, while the Obama and Clinton armies burrow ever deeper into their respective trenches, emerging every so often to impale themselves on barbed wire, generally mimicking the bloody stalemate on the western front in World War I.

Given all the baggage bequeathed by George W. Bush, and the voters' traditional preference for a fresh start in bad times, one could not conjure a better Democratic environment, at least in theory. As Larry Sabato, director of the University of Virginia Center for Politics, put it the other day, "based on 220 years of precedent, a McCain win would be a striking repudiation of American history, since no presidential candidate of a two-term incumbent party has ever been elected under this set of severely adverse conditions."

The Democrats, so bedazzled by the choice between a black man and a woman, have been joyfully anticipating that they would write the history of 2008. But if they don't get their act together with all deliberate speed, and tame their latest impulse for self-destruction (last seen in 1968 and 1980), then it is McCain and the Republicans who will be making history this year.

Certainly, a case can be made that Democrats ultimately have little to fear. Some high-ranking party leaders have been taking it out for a spin lately. It goes something like this: "We've been so energized, we've drawn so many new people into the political process, we've raised so much more money than McCain, and when we finally have our nominee, we'll come together as a party, all the energy and enthusiasm will carry over, and we'll unmask McCain as the new Bush."

Presumably, once the Democrats are training their fire at McCain rather than at each other, they can drive down his poll numbers by reminding swing voters that he's not just a war hero - that, in fact, he has supported the privatization of Social Security (a Bush fiasco that was scrapped in 2005); that he's a free-trader with little concern for protecting domestic workers; that he now wants to make permanent the Bush tax cuts for the affluent, the same tax cuts he once voted against; that he opposes universal health care; that he wants to cut corporate taxes, a move that would cost the U.S. Treasury an estimated $100 billion a year; that he has been wearing rose-colored glasses on Iraq ever since 2002, when the Bush team started beating the drums for war.

Well, maybe. I seem to recall that voters elected Ronald Reagan in 1980 even though they disagreed with him on a broad range of issues. He took his hard-core conservative base (roughly 30 percent of the electorate), added enough independent swing voters and disgruntled Democrats (roughly 20 percent), and voilà. That's the McCain blueprint, by the way: Hold the base, bring in the independents who admire his character and find him likable, and seal the deal with some disgruntled Democrats.

This can definitely be done, especially in the wake of a Democratic implosion. The Pennsylvania primary made that prospect more likely by perpetuating the stalemate, by further exposing the party's schisms.

Now, Clinton and Obama will inflict themselves on the voters of Indiana and North Carolina and continue to make themselves less attractive to the general electorate. Obama's weakness among working-class whites - glaringly exposed in Pennsylvania - raise questions about his viability in Rust Belt swing states. Clinton's incessant attacks may have helped her win Ohio and Pennsylvania, but they have come at a price - driving up her negatives in the national polls, broadening the perception that she is untrustworthy, and generally damaging her standing with independents who like McCain already.

And the longer Obama and Clinton battle, the more invested in victory - and resistant to unity - their partisans will become. Right now, as many as 25 percent are vowing to support McCain or stay home in November if their candidate is denied the nomination. Some of that is probably just angry talk, the kind that is cheap in April. I suspect we'll know more in June. If the primary season concludes with a scintilla of clarity, perhaps the fence-sitting superdelegates will tilt decisively and end this thing.

But if there is no clarity in June, and if (for example) Clinton spends the summer grasping and clawing at a wounded Obama, like the Terminator after its skin had been stripped and its legs blown off . . . well, we know what could happen at convention time, and beyond.

Democrats are probably in no mood to take advice from a founding Republican, but Abe Lincoln's famous warning to the nation seems apt at the moment. He said, "A house divided against itself cannot stand." And he would know. He was instrumental in consigning the fractious Whigs to the dustbin of history.