Is Romney Being Baited?

Perry goes Bruckheimer with a new negative ad:

Romney is hitting back with a negative ad of his own and an anti-Perry website, on top of the frequent attacks during debates. Nate Silver thinks Romney targeting Perry is a mistake:

Mr. Romney is right if he thinks that Mr. Perry remains the biggest threat to taking the Republican nomination from him. I say this as someone who takes Herman Cain’s chances fairly seriously and recoils at the frequent assertions without evidence that he has no chance of winning the nomination. But Mr. Perry’s advantages in terms of the fundamentals — his fund-raising, his respectable number of endorsements, his credentials and experience — are enough to outweigh Mr. Cain’s edge in the polls, especially at a time when most voters remain weakly attached to their current choices.

But it is precisely because Mr. Perry is the more threatening candidate that Mr. Romney might want to think twice about helping to position Mr. Perry as the "anti-Romney" choice …