Jeb Bush brought this one up again at the debate.
The talking point is that if we pause Muslim migration, we'll somehow fracture the "coalition" against ISIS.
Now to the extent that this coalition even exists, it consists of Muslim countries that do not offer equal rights to Christians. Some countries on the coalition list, e.g. Saudi Arabia, outright bar non-Muslims from entire cities and forbid the building of churches.
Somehow this doesn't fracture the magic coalition. And yet if we pause Muslim migration, it will.