Post debate, some ask: What happened to the charismatic Obama of 2008?

In the wake of Wednesday's listless debate performance, Democrats and Republicans alike have been speculating about why Barack Obama may seem different from four years ago.

In the wake of his widely panned debate performance, President Obama has taken to arguing that the man he faced onstage – the insistently moderate-sounding candidate who said he believes in regulation and won’t reduce taxes for the wealthy – was not the “real” Mitt Romney.

But in many ways, Wednesday’s debate has raised an equally uncomfortable question for Democrats: Was that the “real” Barack Obama?

Certainly, many supporters saw Mr. Obama's debate performance as an aberration. And perhaps it was just a bad night: He was out of practice for debates; he was tired. (Former Vice President Al Gore even speculated that the altitude got to him.)

But it came on the heels of a convention speech that also struck many viewers on both sides of the aisle as strangely flat and pedestrian. And few would dispute that Obama's entire 2012 campaign has felt relatively small and tactical – and far less inspirational – compared with the race he ran in 2008.

Which has got some members of the chattering class wondering: What, exactly, happened to the candidate who just four years ago filled stadiums and moved an army of supporters with his soaring speeches and charisma?

Republicans have one answer: essentially, that the emperor has no clothes. Back in 2008, they argue, Obama’s supporters were simply projecting what they wanted in a candidate onto a man who was, in essence, nothing but a blank slate. Now they’re learning the truth. “Obama just isn't that good,” conservative columnist Charles Krauthammer writes. “Not without a teleprompter. He's not even that good at news conferences – a venue in which he's still in charge, choosing among questioners and controlling the timing of his own answers.”

Democrats have a different theory about what happened to Obama: the past four years. Presidents are never exactly the same when they run for reelection. And when they’ve weathered a first term as difficult as Obama’s – managing two wars, a recession, and a stagnant recovery – it inevitably takes a toll. It changes the man.

“Whoever Obama was when he was elected president has been seared away by two active wars, the more free-ranging fight against al-Qaeda, the worst economic crash since the Great Depression, and the endless grinding fights with Washington Republicans – and even, I am sure, activists in his own party,” wrote The Atlantic’s Garance Franke-Ruta. “His supporters keep wanting Obama to be who he was in 2008. But that's not who he is anymore.”

Of course, the Obama who's been out on the campaign trail doesn’t always seem that different from the Obama of 2008. He still can give a rip-roaring speech and fire up crowds. And just in the past few days – perhaps jolted by the poor debate reviews – he seems to have harnessed more of the old energy and zeal.

More to the point, his 2012 campaign was never going to be a replica of 2008. The “change” slogan works well for challengers, but incumbents, obviously, have to argue for continuity. In his case, Obama’s “continuity” argument has been particularly complicated and weighed down by the slow-growing economy.

So the president has had to strike a tricky balance between campaigning with spirit and gusto and acknowledging the sober realities that challenge many Americans. More than anything, it may be that kind of split-personality messaging that has led to the split-personality candidate we’ve seen throughout this campaign cycle.

If he wants to win, however, at this point he clearly has to lose the “grim Obama” who showed up onstage at the debate. As every political consultant will tell you, even in hard times, Americans want to see a candidate who’s optimistic, who has a spring in his step. On Wednesday, that was Mr. Romney. Obama had better hope he can seize that mantle back.