He really should be at better than single-digit leads against also-rans in a state he won by 12 points.
He's under water with independents, at 42/53. And he's lost a lot of support with Democrats, only 78% of whom approve of him with 17% disapproving. He's also at 6/94 with Republicans, but that's pretty much par for the course. His hopes for any meaningful amount of crossover support faded a long time ago. While Obama's in good standing with Hispanics and African Americans in the state, he's at a woeful 36/61 with white voters, mirroring his trouble with them nationally.
There's only one spark for optimism here. Nevada's a hard state to poll, and polls often underestimate Democratic support. The final polls in Nevada's 2010 U.S. Senate race had Sharron Angle winning by 3 points; Harry Reid beat her by 6 points. The final polls in the Obama-McCain race had Obama winning by 7, and he easily beat that spread. But in the first case you had a Republican ticket that was imploding fast, and in the second you had one of the absolute worst statewide candidates of the year against a flawed but wily incumbent.