Nate Silver has a characteristically interesting look at the numbers behind the new Gallup poll giving Perry an early 12-point lead over Romney. Silver makes a couple of good points about the dangers to an early Perry surge–first and foremost, a win in New Hampshire that could encourage party elites to drop Romney.

But I believe Silver vastly understates another danger for Romney, which may tempt Romney into a false sense of security but which represents a time bomb the campaign will have to defuse as early as possible–if possible, that is. Silver writes:

Mr. Romney should have a fair amount of breathing room since the Republican field is heavily tilted toward very conservative candidates like Mr. Perry. Were Rudolph W. Giuliani or Chris Christie to enter the race, Mr. Romney might face a bit more pressure, as he would if Jon M. Huntsman Jr. were somehow to surge. Still, the conservative part of the Republican field is far more crowded, and will be even more so if Sarah Palin runs.

But that should be cold comfort to Romney. Later in the post, Silver mentions Romney’s lead over Perry in New Hampshire is substantial, but if you add all the other candidates to Perry’s total, Perry would lead. So if Perry knocks out other candidates after Iowa, New Hampshire could immediately become a close race. The unstated point is the risk Romney may be approaching his ceiling of support. Perry, on the other hand, may just be getting started.

Look at that Gallup poll. As I wrote yesterday, Perry is easily holding his own constituency while encroaching on Romney’s. I understand national polls are less important than state polls at this point, but the trend is there. Ron Paul will probably stay in the race for a while, but Bachmann’s 10 percent may be up for grabs. Expect it to go to Perry. Herman Cain is next, with 4 percent. Cain’s claim to fame has always been his early–very, very early–opposition to government-run national healthcare, so it’s doubtful his support goes to Romney, but perhaps his business credentials will throw Romney a bit of it. After Cain, we have Gingrich; Romney and Perry could split those votes. Santorum’s 3 percent probably goes to Perry. Huntsman’s 1 percent presumably goes back to Obama for the general election.

So what happens if we see national polls giving Perry a lead of 25 points or more? And all that assumes Perry won’t siphon away more of the moderate vote, which he is very likely to do if this keeps up. The state polls right now are Romney’s refuge, but Perry has a built-in advantage. The sooner other candidates exit the race, the worse Romney’s chances look.