Politics ordinarily has a certain predictability. Yet presidential politics this year has often seemed to resemble what science writer James Gleick described in his book "Chaos."

"Chaos," he quotes one physicist as saying, "eliminates the Laplacian fantasy of deterministic predictability." Time and again this year, unpredicted and seemingly unpredictable developments have reshaped the presidential race. And they don't appear to stop coming.

At the beginning of the year, things seemed fairly simple. Democrats had a big lead in party identification and appeared headed to victory. Democrats seemed likely to settle on a nominee quickly, while Republicans were predicted to be heading for a long, drawn-out primary fight. But three developments changed the shape of the race, to the benefit of Republicans.

First, John McCain clinched the Republican nomination early, while Democrats suffered through a protracted battle between Hillary Clinton and Barack Obama. With help from the Republicans' winner-take-all delegate allocation rules, McCain was able to convert razor-edge victories in primaries to an unassailable lead in delegates. Over the objections of radio talk-show hosts, Republicans nominated the only candidate, it seems in retrospect, with a chance to win. Meanwhile, Democrats clashed in tribal warfare that inevitably left some in the party unhappy with the nominee.

Second, the success of the surge strategy in Iraq managed to penetrate through a media blackout to the voting public. This undermined the appeal of Obama's call for rapid withdrawal. Obama still can argue that he was right in opposing the war. But McCain can argue that he was right in supporting the surge and that Obama was wrong in opposing it and predicting it would fail. An issue that looked like a big negative for McCain now looks to be a wash.

Third, $4-a-gallon gasoline converted voters from opposing offshore oil drilling to supporting it. McCain nimbly switched. Congressional Democrats dug in their heels and blocked a vote on the issue, then beat a partial retreat. Obama was stuck on the short side of public opinion.

Political maneuvering further evened the scales. After the McCain campaign pointedly made fun of the grandiosity of the Obama campaign, Obama cast his acceptance speech as a partisan attack rather than an appeal to what Americans have in common. McCain, by choosing Sarah Palin, invigorated the party base and put energy and his maverick reformer role on the front-burner.

But chaos, it turns out, does not favor just one side. The credit crisis in the last two weeks of September raised an issue that has, so far at least, helped Obama. McCain railed against Wall Street and called for the firing of Securities and Exchange Commission Chairman Christopher Cox. Obama argued that the crisis showed the failure of Reaganite deregulation. Continued...