Every time I see it I check the aggregates. RealClearPolling for the Republican bias, Nate Silver for the Democrat bias. In both cases, the headline seems credible but unremarkable, he's been ticking slowly downwards since he was elected, but in both cases he's also been lower the last time he was president.

Right now, Nate Silver has him at 39.7 while RCP have him at 41.6