The Palin bump was destined to end sometime, and with Rasmussen showing the race now tied, the bounce appears to have run its course. But I would note another factor — in just about every appearance [except for 9/11] Obama and Biden have been on the attack. (This isn’t a complaint, just a statement of fact.)

Yet the attacking tone is not, so far, dramatically affecting how people feel about Obama. From the CBS poll that shows Obama ahead, 48-43:

Voters’ opinions of the candidates have changed little since last week, and both hold similar favorable/unfavorable ratings. (Obama’s favorable stands at 45 percent and his unfavorable at 35 percent; McCain’s favorable is 44 percent and his unfavorable 37 percent.)

Usually, going negative carries a cost for a candidate. So far, Obama has avoided paying that price.

UPDATE: When 77 percent of your ads are negative, as Obama’s were last week, that’s going to have an impact. Only 56 pecent of McCain’s ads are negative by comparison.