Nothing explicitly prevents it. It doesn't really matter anyhow; Congress has the exclusive power to impeach. Impeachment is the mechanism the constitution provides deal with criminal presidents and the president can't block it.
Make no mistake; the last thing Comey and Clinton+Obama et al. wanted was to fill news cycles with "FBI investigation reopened" 11 days out. It's bad, whatever it is, and this is a CYA move; Comey believes he needs to be able to claim he notified Oversight and made this public prior to the election.
Nothing explicitly prevents it. It doesn't really matter anyhow; Congress has the exclusive power to impeach. Impeachment is the mechanism the constitution provides deal with criminal presidents and the president can't block it.
Make no mistake; the last thing Comey and Clinton+Obama et al. wanted was to fill news cycles with "FBI investigation reopened" 11 days out. It's bad, whatever it is, and this is a CYA move; Comey believes he needs to be able to claim he notified Oversight and made this public prior to the election.