Editor's note: Gloria Borger is a senior political analyst for CNN, appearing regularly on CNN's "The Situation Room," "Campbell Brown," "AC360°" and "State of the Union With John King," as well as during special event coverage.
(CNN) -- The moment has to happen sometime in a new administration, and the Afghanistan speech was it: the end of the Obama campaign of limitless aspiration and the acknowledgement of a presidency burdened by harsh realities and difficult choices.
The candidate who had called the surge in the Iraq war "reckless" was proposing a surge of his own in Afghanistan.
The candidate who criticized President George W. Bush's emergency spending bills for the Iraq war could end up proposing one of his own.
The candidate who said that defined benchmarks -- and penalties -- were necessary for Bush's surge to work in Iraq provided none of his own in his speech.
Yet, in the end, there was one consistency: The candidate who called Afghanistan a "war of necessity" found that, as president, he still believes it to be true.
There was a clear subtext in the president's speech on Afghanistan: I wouldn't be in this awful situation if my predecessor hadn't sent troops to fight the wrong war in Iraq. It's awfully late in the process to jump-start this war. I tried to figure out some other way to approach this, driving my generals and the intelligence community to distraction for three months with all of my questions and scenarios. No one can actually be certain that this is going to work, given the fact that we have to depend on the previously -- and notoriously -- untrustworthy governments in Afghanistan and Pakistan.
But, knowing the threats that are out there, we have no choice: "If I did not think that the security of the United States and the safety of the American people were at stake in Afghanistan," Obama said, "I would gladly order every single one of our troops home tomorrow."
But he found out that he could not. Nor could he go the leaner troop route initially proposed by Vice President Joe Biden.
Obama himself made it clear that Afghanistan is no Vietnam: After all, our enemies there weren't looking for ways to kill Americans at home. And, by specifying a clear exit ramp, he made it clear that he isn't about to get bogged down in a war, as if saying it could make it true. Or at least convince his liberal base to support him.
Yet what he couldn't escape were the comparisons that he might be morphing into a version of Lyndon Johnson: a president with a robust domestic policy agenda fighting an unpopular war at the same time. And you can just hear his argument: I'm not LBJ; we're not getting bogged down. We're getting in fast, and, after 18 months, we're gone.
But, like LBJ and Vietnam, this is now Obama's war. It's also Obama's economy -- and his high unemployment, his health care bill, his deficit.
He's all-in. And now, so are we.
The opinions expressed in this commentary are solely those of Gloria Borger.