Donald Trump has vowed to intensify his crackdown on immigration if he returns to the White House and has left the door open to resuming his most controversial policy - family separations at the U.S.-Mexico border - but key allies who could join a new Trump administration as immigration enforcers are wary.

Five former Trump officials and conservative allies told Reuters that even as Trump weighs harsher anti-migrant measures, they are concerned about implementing a new version of the 2018 “zero tolerance” policy that separated thousands of children from their parents at the southwest border.

They said they worry about a repeat of the widespread public backlash provoked by the original policy.

“The family separation that resulted from the zero tolerance caused an uproar in the country,” said Tom Homan, a former Trump immigration official who could join a second administration. “The best way to do it, rather than deal with all that chaos that comes with it, is to keep them in a residential center together and have their hearings together.”