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“Well, Governor, we also have fewer horses and bayonets, because the nature of our military's changed. We have these things called aircraft carriers, where planes land on them. We have these ships that go underwater, nuclear submarines.”

-- President Obama in the final presidential debate.

President Obama needed a knockout performance in his final debate with Mitt Romney, but instead managed to reinforce the trend line of the election.

Obama avoided what might have been a disaster on the top task in any president’s job description and achieved a win on points on his strongest suit in the election. Those are good things.

But neither did he do anything in his larger goal for the night: to show voters that Romney was unfit for command. Romney again came through looking plausibly presidential and said or did nothing to suggest to voters that he would be a danger to national security.

With just two weeks to go and the race shaping up in Romney’s favor, Obama needed something to reset the trajectory of the contest. Obama’s aggressive performances in Monday’s foreign policy debate and in last week’s town-hall debate were intended to do something to knock Romney out of the saddle.

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The contempt in which Obama holds Romney was never more evident than it was last night. As he glared and mocked, attacked and derided, Obama was hoping that voters were sharing in his disdain for the Republican nominee.

And while polls show that Obama got the advantage on Romney when it comes to being to talk about the job of navigating a treacherous world, the same polls also showed that Romney was seen as a perfectly plausible commander in chief.

In fact, Obama’s attacks, delivered through gritted teeth, tended to reinforce the placid Romney’s status as the frontrunner.

Romney holds the advantage on the top concern of voters this year: the anemic economy. All he needed was to pass the plausibility threshold on being commander-in-chief, as reflected in his cautious approach on Monday night. And as the president himself might say: “You’re plausible enough, Mitt.”

The central thrust of Obama’s campaign over the span of nearly seven months has been that Romney is an unsuitable alternative. Unwilling to take a chance on unveiling a second-term agenda, Obama has continued trying to ruin Romney in the closing weeks, doubling down on the “kill Romney” strategy that has largely animated Obama’s re-election bid. But Romney, who made himself more than plausible in their first debate, has only grown in his stature as an acceptable alternative to the embattled president.

Both campaigns play it safe with their forecasts for the election – hard-fought, narrow contests in just a handful of swing states – but the danger is growing for the president of a substantial loss. Having opted to withhold much of his vision for a second term in favor of an effort of making the election a referendum on his challenger’s character, what’s an incumbent to do if the challenger survives the onslaught?

With just two weeks to go, it’s too late for Obama to change his course. But it’s also hard to imagine his current strategy working without a howitzer-sized October surprise. Unless Obama has video of Romney actually engaging in vampirism or cackling as he rolls around like Scrooge McDuck in a pit of Swiss Francs, what could Obama say or do that would cause voters to listen?

The reality of Romney has fallen so far from the scary, corrupt character depicted by Team Obama, that the incumbent has lost much of his credibility to tell voters much at all about the challenger.

Two weeks is a long time in politics, and certainly an international crisis, an attack on the homeland or a truly shocking revelation about Romney could change the trajectory.

But given the current cacophony of attack ads and the dueling daily messages from both campaigns, it’s getting harder to imagine where another big trajectory change in the race could arise.

And Now, A Word From Charles

“I think what is happening tonight is that Romney has momentum.  And as long as he draws even tonight, he doesn't even have to win.  If he draws even tonight, the momentum continues and I think that would carry him to a victory.  So he just has to hold serve.  He doesn't have to hit a homerun to make seven sports into one metaphor.”

-- Charles Krauthammer on “Special Report with Bret Baier.”

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Chris Stirewalt is digital politics editor for Fox News, and his POWER PLAY column appears Monday-Friday on FoxNews.com. Catch Chris Live online daily at 11:30amET  at  http:live.foxnews.com.