The Daily Caller alleges that 30 countries refuse to take back their citizens who, as illegal immigrants to the U.S., were convicted here of crimes. It continues that U.S. law permits us to refuse issuing visas to citizens of such nations, but that we are not doing so - not enforcing our law, not withholding visas.
If true, it is something President Trump should get T-Rex to reverse at State. I'm positive at least some of the refusenik nations would reverse their policies.