President Obama's approval rating has hit an all-time low of 39 percent, dropping below 40 percent for the first time in Gallup's daily tracking poll. The setback comes just as Republican efforts to pick a 2012 challenger are picking up steam, with Rep. Michele Bachmann winning the momentum-building Iowa straw poll and Texas Gov. Rick Perry making a long-awaited entry into the race. What are political analysts reading into Obama's falling numbers? Three theories:

1. Blame the economy
"Obviously this is largely a reflection of the state of the economy," says Doug Mataconis at Outside the Beltway. Obama's approval ratings spiked to 53 percent after Osama bin Laden was killed, but they've been trending lower for two months. Obama sank into the low 40s during the debt ceiling fight and, unless the picture brightens, the numbers could get even worse than this.

2. Democrats are realizing Obama isn't The One
"My hunch is that heart-achy Democrats are driving this," says Ed Morrissey at Hot Air. Seven in 10 voters in the president's party still want him as their nominee, but that's down 11 points since June. One reason for that is "Democratic disgruntlement over the debt-ceiling deal," but there are plenty of other factors causing Obama's base to sour on his leadership.

3. Obama is down, but not out
The "political environment" is not being kind to Obama right now, says David Paul Kuhn at RealClearPolitics. But this doesn't mean he's toast in 2012. Obama is far from Jimmy Carter territory — that former president's numbers were in the low 30s and high 20s in 1979, "and Carter still made a race of it." Once the GOP picks its challenger, that person will be vulnerable, too. "Even Superman had kryptonite."