President Obama was on the ropes in the polls after the first presidential debate. After the second presidential debate, he hit the mat in the polls. And after the third presidential debate, he looks to be down for the count.

The question, of course, is why.

Looking at the debates alone doesn't tell the full story. Romney surely won the first debate -- in fact, he cleaned President Obama's clock -- but in the second debate, he fought President Obama to a draw. And in the third and final debate, which centered on foreign policy, Romney pulled his punches.

So just what happened to change this race from an Obama blowout in late September to a substantial Romney lead in late October?

The American public got serious. And President Obama got unserious.

In any presidential race, the candidate who is perceived as steadier will generally win. Jimmy Carter blew the perception that he was a steady hand with his "malaise" speech and his wild attacks on opponent Ronald Reagan. Bill Clinton, despite his personal foibles, made Americans feel steadier than the flailing Bob Dole. George W. Bush looked like a steadier and more trustworthy leader than the king of flip-floppers, John Kerry. And in 2008, Barack Obama seemed to be more even-keel than the wildly gyrating John McCain.

In today's race, there is one candidate who seems steady, whose presence calms voters. And there is another candidate who seems petty and vindictive, who wanders from odd slogan to odd slogan, who attacks his opponent relentlessly. The former is Mitt Romney. The latter is Barack Obama.

That's what has been on exhibit for the last month. Mitt Romney continues to press home his case on Barack Obama's failed economic plans. He continues to make his case for a larger vision of American power in the world, especially by boosting our economic competitiveness.

Meanwhile, Barack Obama minimizes issues. The candidate who promised us that he would heal the planet in 2008 now can't see beyond his teleprompter. If Mitt Romney wants to talk about cutting spending, Barack Obama wants to talk about how Big Bird will get hurt. If Mitt Romney wants to talk about our failures of security in Libya, Barack Obama wants to talk about how the deaths of Americans are "not optimal" and "bumps in the road." If Mitt Romney wants to talk about our military readiness, Barack Obama wants to talk about whether we ought to cut bayonets.

Obama is now channeling Gloria Swanson in "Sunset Blvd": "I am big. It's the campaign that got small." But in truth, Obama isn't big. He never was. He was the "Wizard of Oz," hiding behind the curtain provided to him by the media. All of his promises meant nothing. What does it mean to heal the world? What does it mean for the waters to recede? What does it mean to provide hope and change?

It means nothing. And when Obama put his big ideas into action, all the American people saw was petty infighting, gargantuan new webs of bureaucracy, and a president left blaming his predecessor for all his problems.

Obama's presidency reflected his poverty of ideas. Now his campaign does, too.

A small campaign means an unstable campaign. When you're forced to jump topic to topic, debating inconsequential ideas with gusto, your campaign seems to swing unpredictably back and forth. When you're discussing Romnesia one day and binders the next, you're losing.

A big campaign, by contrast, has big themes. Obama has no themes because he has no record and no second-term agenda. Romney has themes: economic growth through tax cuts and less burdensome regulation, a foreign policy based on a stronger military. Because he has themes, he seems steady.

And that's why he will win. None of this is going to change in the next two weeks. Obama's record will not suddenly allow him to become an ardent advocate of his own job performance. And he won't come up with any bold new plans -- he has nothing left in the tank. The ball is in Mitt Romney's court. And the American people know it.