Foreign carriers, in and of themselves, generally cannot fly point-to-point U.S. domestic flights. Such practice is called
cabotage. However, from review of this DOT page, cabotage apparently is allowed under certain circumstances. I don't know of any instances; maybe others might know of some. Under the scenario you described, though, it seems hard to imagine that the government would authorized foreign carrier cabotage.
Now, if carriers start leasing foreign crews to fly their U.S. aircraft because they work cheap, that would be a horse of a different color.
