Illegal entry is a misdemeanor, thus criminal. QED.

Still, it seems like a rather desperate rhetorical move to describe even a reckless driver as "a criminal, by definition", much less a person fleeing political persecution and seeking refuge in another country — a right guaranteed to them by international law, even if the US is abrogating its obligations under that law. Technically, it's true that under US law they are guilty of a misdemeanor, just like a wino getting drunk in the park, but clearly neither of these is a central example of the class of people to which we normally refer when we say "a criminal"; it seems more like an argument for disregarding US law.