That's the claim Chris Matthews made on Hardball last night, and it's been a common one in recent weeks as pundits continue to pronounce that the BP disaster has taken a steep toll on Obama's standing with the public. Indeed, as Jamison noted this morning, Dick Morris is pushing the wild theme that Obama's support is “hemorrhaging.”

From Hardball:

Note how Matthews pointed to this chart from Pollster.com to demonstrate Obama's steadily falling approval raring:

Case closed, right? Sure you could debate the “steadily” part of Matthews description, since it appears from the above chart that Obama's rating only began its slight dip in late May, not late April when the spill occurred. Still, looking at the tail end of the chart where the “approve” line dips, and the “disapprove” line rises, it seems clear there's been negative movement for Obama since the BP spill in late April. Right?

Not quite.

The Pollster.com chart, which takes into account scores of polling firms and their on-going results, includes the GOP-friendly Rasmussen poll, which posts Obama approval ratings everyday and therefore is given more influence. But what if you remove the Rasmussen numbers from the Obama pile, what kind of job approval picture do you get? After all, scores of big-time news organizations refuse to use Rasmussen iffy data and industry pollsters are on the record as saying they don't trust Rasmussen's robo-call methodology. And, of course, it's a well known fact that Rasmussen's results almost always undercut Democrats by a good five or six points.

So what does Obama's job approval rating picture look like without Rasmussen? It looks like this:

Without the Rasmussen numbers it's suddenly much harder to claim that Obama's approval rating has been “falling steadily” since the BP oil spill. (Does a two to three-point dip as measured by polls that have a margin of error of three points qualify as “falling”?) Instead, Obama's approval rating has remained amazingly consistent, given the avalanche of media attacks the White House has been subjected to with regards to the spill.

UPDATED: Here's Obama's approval rating since April, minus the Rasmussen numbers: