When Mitt Romney started looking like this year’s probable Republican nominee (in fact, way back in 2007, during his first presidential run), I, along with many others, assumed that were he to make it to the general election, one of the main attack lines would be that he’s a flip flopper. In 2004, the Bush reelection team brilliantly exploited John Kerry’s policy reversals to help make the case that he couldn’t be the sort of steady leader that Americans needed in their president, especially during a time of war. Given that Romney had a moderate record as governor of Massachusetts and then had to remake himself as a conservative to win the GOP nomination, it seemed natural that Obama would jump on the “flip flopper” narrative. But much to my surprise, his campaign chose not to.

This is no accident. Back in April, the Politico’s Glenn Thrush and Jonathan Martin reported that none other than Bill Clinton convinced the Obama team to steer clear of the “flip flopper” argument in favor of portraying Romney as somebody who had embraced “a brand of tea party conservatism that turns off Hispanics, women and moderate independents.” The strategy of trying to portray Romney as some sort of an extremist seemed to be going smoothly as Obama began pulling away in polls in early September after the Democratic National Convention. Yet the plan had one flaw that could yet prove to be fatal. With a single debate performance, Romney was able to undo much of the damage inflicted by Obama’s campaign for months, simply by not living up to the caricature that had been invented for him.

Over at the Washington Post, liberal Greg Sargent has insisted that the Obama campaign can hit Romney on both fronts. “There seems to be a debate underway over whether the Obama campaign should portray Romney as ‘severely conservative’ or as a ‘flip flopper,’ with some noting that these are at odds with each other,” he wrote. “But really, there needn’t be any conflict here. Romney took a number of positions to get through the primary that are extreme. He is now trying to obscure and moderate those positions to win the general election. One can point both of those things out without contradiction. And by the way, this is true on issue after issue after issue, from abortion to tax cuts to immigration.”

There are two main problems here. Firstly, narratives take time to build, and it would be harder for the Obama campaign to start hammering Romney as a flip flopper now than it would have been had they started doing it months ago. Secondly, in practice, it’s not as easy to thread the needle between the “flip flopper” attack and the “extremist” portrait than Sargent makes it seem. For instance, showing clips of Romney shifting stances on abortion would mean drawing attention to his pro-choice past in Massachusetts. That makes it a lot more difficult to convince Americans that he’s some sort of radical who wants to ban birth control and commandeer lady parts.

We’ve seen the Obama campaign attempt to argue along the lines suggested by Sargent, with various statements about Romney “hiding” his truly extreme positions. But ultimately, charging that he has deeply held extreme positions undermines the attempt to portray him as a flip flopper.

Obviously, Obama may very well still get reelected. But if he loses, I imagine his failure to exploit the “flip flopper” attack will probably be looked back upon as one of his key mistakes.