Obama approval holds steady despite BP spill. Why?

This is Gallup's tracking poll since January.  Pretty hard to discern any meaningful trend.  You certainly would be hard pressed to pick out any evidence of a BP-disaster effect.

Nate Silver notes that even on the narrower question of Obama's handling of the disaster — [I only used "spill" in the headline this one time so it would fit on one line:] — Obama's numbers are flat if not slightly rebounding:

Because this seems counterintuitive it has led to much perplexity.  Silver writes:

1) Obama is...