What a difference one month can make.

In October, Democrats built up an enormous lead in generic ballot polls, and seemed poised to make big gains in the next elections. Yet Republicans have already bridged the gap, dashing Democrats' dreams of a resounding 2014 mandate.

A handful of polls in the past few weeks have shown Republicans either tying with Democrats or taking the lead in a generic face-off. In the latest such survey, released Tuesday by CNN, Republicans edged out Democrats by a 49 to 47 percent margin. That was a net 10-point swing from one month ago, when Democrats boasted a wide 50-42 lead.

So what happened? In a word: ObamaCare.

In the immediate aftermath of the government shutdown, Democrats were well over the threshold on the generic ballot to retake the House — a 6.8 percent edge, according to Cook Political Report's David Wasserman. Then the Affordable Care Act debuted in spectacularly terrible fashion. The federal exchange site crashed; Obama's promise that people could keep their insurance proved wildly false; and Democrats turned on the administration while running for cover.

Add a GOP-friendly election map and the fact that the president's personal brand has been badly tarnished, and you have the perfect recipe for "another midterm nightmare" for Democrats, wrote Roll Call's Nathan Gonzales.

Not coincidentally, Republicans are ramping up their critiques of the health care law with an eye toward 2014. As the New York Times detailed last week, Republicans even have a playbook ready for attacking the law as a failure and Obama as a liar.

Unless ObamaCare starts to work better, that kind of messaging will be a highly effective weapon next year.

The good news for Democrats is that the next elections are a year away, an eternity in politics. And as the past month has shown, public opinion can turn on a dime.

In addition, there are already signs that the health care law is beginning to improve. Obama said Monday that the troubled federal exchange marketplace was "starting to work pretty well now," and state-run exchanges have quietly been picking up steam, putting them on pace to hit their enrollment targets.

Moreover, generic ballot questions should always be viewed with some skepticism. Bashing Democrats today is one thing, but voting them out on Election Day is another. And Republicans have yet to repair their standing following the disastrous shutdown, so it's not like voters are rushing to embrace them as a great alternative.

A GOP wave in 2014 is thus "highly unlikely," wrote election forecaster Charlie Cook, because "voters hate Democrats in Congress while simultaneously despising Republicans."

"To vote against one party, people have to vote for another in very large numbers, which at this point seems unlikely," he added.

Democrats' huge edge last month was clearly unsustainable. Still, it's shocking to see how swiftly the party's lead evaporated over the course of one (really, really bad) news cycle.