It must suck to be Barack Obama, and see your lead go up in smoke.

A poll released today by CBS News reports that Barack Obama's post-Democratic convention bounce has been erased — and that for the first time, John McCain has drawn even with his Democratic opponent in the network's poll.

Only hours before McCain accepts his party's nomination in what will likely be the most-viewed moment thus far of his presidential bid, the race is knotted at 42 percent apiece, with 12 percent of voters stating that they are undecided, according to CBS. Obama was ahead 48 percent to 40 percent by CBS’ measure following the Democratic convention.

Other polls have failed to show the same tightening of the race found by CBS. Neither the Gallup or Rasmussen daily tracking polls have registered a significant drop in Obama’s support from his post-convention bounce numbers. The Gallup tracking poll, for example, still has Obama ahead of McCain 49 percent to 42 percent.

CBS’s findings from Monday to Wednesday — covering the early days of the Republican convention — is particularly noteworthy because generally Obama runs stronger in the CBS poll than in other surveys.

That last paragraphy is why I bothered with this story. This poll is the one he usually does best in, and it now shows the race knotted. Is it an outlier? Or a harbinger of where the rest will go in the next few days?