Because gaffes never matter -- until, of course, they do.
Although the kerfuffle over hidden-camera footage of Mitt Romney shows no signs of subsiding yet, some cooler heads are already arguing that the impact of the film has been overestimated. National Journal's Ron Fournier, for example, pulls out five strong reasons why the Republican could still win the race.
Let me add one more: because gaffes never matter. Political scientist John Sides put together this chart at the Monkey Cage showing how the polls reacted to previously declared major gaffes of the campaign season -- "you didn't build that," "doing fine," etc. Or more accurately, it shows how they didn't react. It appears that few voters are really changing their mind because of some single, ill-advised comment that a candidate has made. More recently, Obama's numbers actually decreased after Romney's previous, allegedly catastrophic gaffe, this one about attacks on the U.S. embassies in Libya and Egypt -- although that probably reflects the air coming out of the president's convention bounce, not public reception of foreign events.
Of course, this is nothing new. Perhaps the most famous example of a campaign-derailing gaffe came when Romney's father George claimed he'd recevied a "brainwashing" by U.S. generals while in Vietnam. But as Benjamin Wallace-Wells noted in a stellar piece on Romney '68, the candidate was already fading fast when he made the comment. Despite the received wisdom, it didn't really spell the end of his campaign. Or take Gerald Ford's disastrous comment, made in a debate against Jimmy Carter in 1976, that "there is no Soviet domination of Eastern Europe." After that remark, Carter took over the lead from Ford, but by late October, the president had pulled back ahead of his Democratic challenger. Ultimately, of course, Carter won -- but the lesson is that the Eastern Europe comment was hardly a silver bullet.
The argument that Romney skeptics -- that is, observers on the left, right, and objective sides who see his path to victory narrowing -- make is that a series of gaffes eventually aggregate in the consciousness of voters to create an image of a bumbler. (National Journal's Alex Roarty lays out the case astutely.)
It may be that the combined effect eventually sinks Romney. But what Sides' graph shows clearly is that we'd be wise not to read too much into this one incident. (Chaser: Read Brendan Nyhan for more on the dangers of judging this incident too fast.)