In sizing up yesterday's tracking polls, which show McCain getting a nice bump out of his convention, Nate writes that "we should probably expect this bounce to get bigger before it gets smaller." That's probably right. After all, tracking polls like Gallup typically combine three nights of polling--yesterday's number reflected Thursday, Friday, and Saturday nights. Since Thursday's polling would have come before the McCain speech, you'd expect the next three-day average--which tosses out Thursday and adds in Sunday, making it the first to cover three post-convention nights--to give him a bigger lead.
That's how conventions have traditionally worked, in any case. On the other hand, this was hardly a typical convention--I'm not sure a vice presidential pick has ever generated as much enthusiasm within a party and as much buzz overall as Sarah Palin. Which makes me wonder whether the source of the bounce is the convention per se, or Palin and her speech. If it's the former, then McCain's tracking poll lead should widen today, as Nate predicted. But, if it's the latter, then we may see it stabilize or subside, since yesterday's tracking poll would have included what are presumably the three strongest Palin days--Thursday, Friday, and Saturday.
Update: The latest Gallup tracker shows McCain widening his lead to 49-44 from 48-45. Rasmussen shows McCain up 1 after being tied yesterday. I'd argue that the bounce has maxed out--the big jump was from Saturday to Sunday, not Sunday to today--but obviously those count as increases. Sunday turned out to be a slightly better day for the McCain ticket than Thursday.
--Noam Scheiber