So, it looks as if Michele Bachmann is going to be a presidential candidate in 2012. Of a sort. She's certainly not running for president in the sense of potentially winning that office (although it's always possible she might believe she can win). She is not, of course, a plausible nominee, much less a plausible winner in November 2012. Members of the House don't get nominated; Members of the House with a history of saying nutty things don't come close to being nominated.
That doesn't mean, of course, that she will have no effect on the contest. Some possible scenarios and consequences:
1. She'll get a fair amount of attention -- as Dave Weigel correctly notes, at the very least a Bachmann candidacy is very good news for the Daily Show and the cable networks.
2. Still, the most likely result is that she'll be like Alan Keyes, B-1 Bob Dornan, and Gary Bauer...capable of making some noise, but eventually garnering well under 10% in early states and promptly disappearing. Remember that the noise a candidate generates is not necessarily related at all to actual votes -- or else Ron Paul would have been a far more serious distraction in 2008 than he was.
3. Also remember: all presidential nomination fields are narrowed, and many contests are decided, before voters get involved beginning in Iowa. Fringe candidates have essentially no effect on that process.
4. If, however, several candidates are plausible nominees but no one has wrapped it up...yes, it's possible that Bachmann could mess with things a bit. Ed Kilgore makes a case that she'll do relatively well, and perhaps if the cards fall just right even win, in Iowa. As I said, I think a sub-10% ceiling is more likely, but it's not implausible that Bachmann could join Pat Robertson as a non-serious candidate who does seriously well in Iowa.
5. If (and note that we're now two deep in "ifs") Bachmann does do well in Iowa, the main effect to watch for is that it pushes someone else out of the top tier there. Kilgore (and Steve Benen) think Tim Pawlenty is likely to suffer...I think there's more uncertainty to that part of it than to any other portion of this speculative chain. I would only say that in an open contest, it would be a severe blow to any candidate to finished out of the top three in Iowa (or in New Hampshire).
6. Also: the debates! Kevin Drum has an excellent item about it. Remember, both Michele Bachmann and Newt Gingrich are basically capable of saying anything at all during a debate, and they will be somewhat harder to just ignore than Alan Keyes was. On top of that you probably have either Ron Paul or Rand Paul, who are slightly more predictable but similarly off-the-wall and disruptive. And Drum missed Gary Johnson, who isn't quite a wacky as Ron or Rand Paul, but still figures to add to the general chaos. Obviously, if the Sage of Wasilla is there, well, there's that, too. Most of what you'll read (not Drum, who gets it right) about the effects of such debates (either on the dynamics of the nomination contest or especially on the effects for November 2012) will be massively overblown, but it sure will be fun if they're all in, and it'll be something of a pain in the ass for the serious candidates.