If Romney relents, it's a big deal for the obvious reason that candidates looks terrible when they backpedal. But it'll also force him to return to old, ineffective themes, or find new and inspiring things to run on, which he pretty clearly doesn't have.
On the other hand if he ignores all the pushback from the press, the political establishment will be facing something very new: a candidate -- not his surrogates or outside supporters, but the top of the ticket -- ignoring fact checkers, traditional campaign reporters, and even a few conservatives, all of whom have determined and publicly declared his attacks false.
That will effectively pit the press against the Romney campaign in a test of will and influence. And it's disconcerting to imagine that a determined media might not be able to effectively neutralize a presidential campaign intent on flooding the airwaves with false attacks. But that's where we might find ourselves in the next couple weeks.
Yesterday I mused that it would be odd if Democrats dedicated the first day of their campaign to attacking Romney, out of context, for saying he likes being able to fire people. Instinctively, I chocked that up to the chutzpah gap between the parties -- to the fact Republicans are often willing to push the envelope farther than Democrats within the bounds of accepted political warfare. On further reflection, I think it seems so unfathomable because we've actually traversed those bounds.
As suggested, this isn't a risk-free tactic for Romney. But if it works, it'll become much harder to identify limits on what campaigns will be comfortable saying about their opponents in the future.