Where's it from: There's been some political glove dropping in the past, but never has the cliche so spiritedly rivaled "the gloves are off" for politics-as-sports-metaphor dominance. So if everyone's just taking off gloves, and in both cases the metaphor is used to indicate that the fight got nasty, what's with the shift? Well, "the gloves come off" has typically referred to boxing, where fighters might remove their gloves to inflict more damage. The idiom to the 1940s. (Boxing itself during the depression.) "Drop the gloves" , where players drop their gloves to the ice as they rush to join a brawl. The idiom gained popularity much later, , which might explain why "the gloves are off" gets so much more play. It's just been around longer.
Why it's catching on: In this case, the shift is almost academic so we primarily attribute today's glove-dropping surge to Fox News. The network hosted last night's debate so others probably looked to their coverage with more frequency giving their preferred headline a little more influence than usual.
Why else? Perhaps more subtly, commentators preferred a hockey metaphor to a boxing one. Sure, when the Republican nominee goes up against Obama in the 2012 debates, a tense exchange of blows might resemble a particularly violent one-on-one boxing match. But last night's debate, with its hodge podge of candidates, in many ways more closely resembled a hockey brawl. It's crowded and unorganized. We just can't wait to see which of the candidates is the first to lose a tooth.