Looks like the syphilis has finally reached Billy's brain.
After that it is a political question. The founders figured it would be obvious to the public that a person of dual or divided loyalties doesn't qualify, no matter when in their lives they held them. But that isn't expressed in the law.
One way to tell that citizenship is important, is that fact that nobody in congress is willing to require everybody in that body to disclose all their citizenship allegiances. When one is outed as dual, it creates a stink. See Cruz and Bachmann. There are probably a couple dozen others, flying under the radar.