COLUMBUS, OHIO - Every week after Labor Day is touted as a critical week in presidential politics. The coming week may actually live up to that characterization.

During the next eight days, President Obama and Mitt Romney will meet for their final two debates -- Tuesday at Hofstra University on Long Island and the following Monday in Florida. At that point, it should be clear whether the momentum that Romney picked up has stalled or whether he continues to gain ground. In the meantime, the front-page headline in Saturday's Columbus Dispatch should serve as a warning to Obama's team. It read, "Romney on the rise in Ohio."

Obama advisers said they believed the post-debate Romney surge had stopped. But virtually every recent poll since Denver, in Ohio and in other battleground states, has shown movement toward the Republican challenger. Obama may still lead in enough states to win re-election, but the margins are no longer comfortable.

The vice-presidential debate did not change the race in any significant way. In fact, it ended up as a booster for both sides. Vice President Joe Biden's aggressiveness cheered Democrats after Obama's lethargic showing in Denver. They believe that Biden dominated and won. Republicans, who saw Biden as overbearing and condescending, came away convinced that Rep. Paul Ryan proved himself more than ready to be vice president. To them, a draw was a victory.

The pressure is squarely on the president Tuesday night, given his performance in Denver. But Romney, too, needs a strong evening to cement the first. His advisers know that if, as expected, the president does a better job Tuesday, stories will inevitably be written about his bounce-back.

Laying out their strategies

Biden laid out the angles of attack that the president will pursue on Tuesday, including confronting Romney about his "47 percent" comment, the percentage of income he pays in taxes, the holes in his tax plan and the GOP ticket's position on abortion. The president's challenge will be to deliver those attacks in a town hall debate that features questions from an audience, a format that generally rewards empathy over aggressiveness.

Romney will be ready to field those attacks in the context of the two broad themes that Ryan hewed to Thursday night. The most important is the argument that the country cannot afford another four years of Obama's economic policies. The second is that the recent attacks in Libya that killed four Americans -- and the administration's changing stories about what happened -- are symptomatic of broader weaknesses in Obama's foreign policy.

Romney has pressed the Libya issue aggressively in recent days, but his advisers are still trying to gauge just how much political traction it may provide. Obama advisers believe it will not be as significant as Romney hopes.

There's one other weakness in Obama's message: the question of what his second-term agenda is. He has been vague about this throughout the campaign, preferring to focus on criticisms of Romney and defense of his first-term achievements. If he has something important to say about a second term, Tuesday night affords him the opportunity to say it.

The last two debates have the potential to change the race again -- and the candidates will prepare accordingly -- but it's likely that the biggest impact has already occurred. Increasingly, both campaigns are focused on the real competition, which is turning out identified supporters and winning over the few remaining undecided voters.

Romney, for example, has been spending much more time in Ohio in an apparent attempt to turn around a state that remains crucial to his White House hopes. He campaigned here Tuesday and Wednesday, he and Ryan campaigned in different parts of the state Saturday, and Ryan will be back Monday.

Who will better motivate voters?

Romney can get to 270 electoral votes without Ohio, but he would have to win Florida, Virginia, North Carolina, Iowa, Colorado, Nevada and either New Hampshire or Wisconsin. In other words, he would have to win just about every other battleground state.

Obama advisers see Romney as a flawed candidate for Ohio: a corporate takeover artist mismatched with a state where the auto bailout, which Romney opposed, has helped boost confidence. But Obama, too, is taking precautions in Ohio. His campaign staffers and volunteers are trying to bank as many early votes as possible, knowing that they have a bigger challenge in turning out their voters than does Romney.

The president will campaign in Ohio the day after the Hofstra debate. And on Saturday, the campaign announced a big rally for Thursday that will feature former president Bill Clinton and Bruce Springsteen -- an event clearly designed to get the president's base to the polls and to win over undecided voters.

The turnout battle will be fierce between now and Election Day. The real question is which side will be more motivated by the time Obama and Romney conclude their face-to-face encounters.