For the third time in this race, Barack Obama headed into election night with the opportunity to deliver a knockout blow to the campaign of Hillary Clinton. And for the third time, he let Clinton escape from the corner to fight another round.

Obama’s first chance came when he rode a wave of change from Iowa into New Hampshire, and opened up a double-digit lead in polls. Then Clinton pulled off an amazing upset. Heading into Super Tuesday, Obama had another chance to send Clinton packing by winning in California or one of the other large states, but he was unable to overcome her built in advantages.

On Tuesday, the story was similar. Though just weeks ago Clinton enjoyed massive leads in Ohio and Texas and the conventional wisdom was that all Obama needed to do was come close enough in the states to solidify his delegate lead, the premature coronation of Obama by the media raised the expectations.

Obama came into last night with a string of 11 consecutive victories, a comfortable lead in the delegate count, and a tremendous money advantage. Suddenly, Clinton pulling off a solid win in Ohio and a small victory in Texas’s primary became enough for her to provide a rationale to stay in the race.

Exit polls showed that late deciders overwhelmingly voted for Clinton. Last week, the Obama campaign charged that Clinton would unleash a “kitchen sink” strategy of attack against Obama in hopes that something would stick, and they were right.

In the build up to Tuesday, the Clinton campaign seized on reports that Obama’s top economic advisor had assured Canadians that Obama didn’t really believe his harsh rhetoric on NAFTA, ran a “red telephone” ad suggesting he wasn’t ready to be commander in chief, and questioned his relationship with the indicted Tony Rezko. This strategy appears to have worked.

“The people of Ohio have said loudly and clearly: we’re going on, we’re going strong, and we’re going all the way,” an exuberant Clinton declared to supporters in Columbus, portraying herself as an underdog who was counted out and “refused to be knocked out.”

At this point Clinton’s rationale for staying in the race is to argue to superdelegates that she has won the major states such as New York, New Jersey, California, Massachusetts, Texas, and the bellwether of Ohio. With Pennsylvania coming up on April 22 — a state that favors Clinton because it is similar in makeup to Ohio and because Gov. Ed Rendell is a strong supporter — she has the chance to pick up another big victory.

Furthermore, with Obama now undergoing media scrutiny for the first time, the longer she hangs in, the more chance there is for something unpredictable to happen that could hinder Obama’s campaign.

THAT DOESN”T MEAN that Clinton doesn’t still have her work cut out for her. Obama is well positioned to win the caucus in Texas that was held after the primary, and may very well come out of the state with more delegates. This Saturday, Wyoming votes followed by Mississippi next Tuesday. Both states fit the profile of states Obama has already won, and offer him the chance to expand his delegate lead. While Clinton may win Pennsylvania, Obama could counter with a huge victory in North Carolina two weeks later.

But what last night made clear is that this will be a bitterly fought race that will continue at least until late April, very possibly until June in Puerto Rico, and perhaps even until the Democratic National Convention in Denver this August.

And if last night were any indication, it could get ugly between the two campaigns, with the potential for lawsuits that could turn the race into a repeat of Florida in 2000. As voting was still going on in Texas, the Clinton campaign held an “emergency” conference call with reporters to discuss voting irregularities in Texas and claim that Clinton supporters were “locked out” of caucus sites by Obama backers. Campaign officials declared “all options are on the table” as far as action they may take to address the problem.

The call became a circus when Bob Bauer, Obama’s general counsel, crashed the question and answer session and demanded that Clinton officials “stop attacking the caucus process that didn’t start bothering the Clinton campaign until it ran a series of fairly extraordinary losses.” A heated exchange with Howard Wolfson, Clinton’s communications director, ensued.

Meanwhile, Ohio Gov. Ted Strickland, who campaigned vigorously for Clinton and is one of her strongest supporters, flashed the nuclear option. Warming up supporters at Clinton’s victory rally, Strickland shouted to cheers, “Let us go to Michigan and Florida.” Clinton won both states, but they were penalized by the Democratic Party for holding their nominating contests too early and stripped of all of their delegates. Candidates didn’t campaign in either state and Obama wasn’t even on the ballot in Michigan.

The issue was supposed to be moot because the Democratic race was supposed to be locked up by now, but with the race dragging on it remains a prominent and barbed issue: Should Clinton be able to rewrite the rules in the middle of the process and allow Michigan and Florida delegates to be seated at the convention even though she agreed to a system under which they would not? Should voters in two major states be denied their right to have their voices heard? What legal issues are raised by having new primaries in the two states?

These questions will be debated in the coming weeks and months. But one thing is for sure. John McCain is one happy man this morning.