A reader sets me to rights:
The word "brit" literally means covenant. The full phrase in this context is "brit milah", the covenant of circumcision. So when it was written "at a Jerusalem brit", it means "at a Jerusalem circumcision."
And while I'm at it, Jules Crittenden is not David Frum's brother-in-law. He's David Frum's wife's cousin. With the neocons, the layers of family connections can get confusing.