"The 14th Amendment is unconstitutional."Of course he didn't say that. What he did say is that the 14th Amendment doesn't obviously grant "birthright citizenship" to "anchor babies". And he's completely correct. The 14th Amendment says:
"All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States"The complicated bit is in parentheses. If you remove that bit, then of course Trump would be wrong, since it would clearly say that being born in the U.S. grants citizenship.
But the phrase is there, so obviously some babies born in the U.S. aren't guaranteed (by the constitution) citizenship. Which babies are those?
The immigration law 8 U.S.C. § 1408(a) lists some of them: babies of ambassadors, heads of state, and military prisoners. [UPDATE: this appears wrong, I saw it in many Internet posts, but it appears to be untrue. But, it doesn't change the conclusion. I'll update this post again when I figure this out].
It's this law that currently grants babies citizenship, not the constitution. Laws can be changed by Congress. Presumably, "illegal aliens" could easily be added to the list.
This would be challenged, of course, and it'd probably work it's way up to the Supreme Court, at which point they'd rule definitively on whether the Constitution grants all babies citizenship. The point is simply that the Supreme Court hasn't ruled yet. Nobody can cite a Supreme Court decision clearly disproving Trump.
Thus, if you listen to Trump's remarks that everyone is criticizing, you'll see that he's right. Not all babies are granted citizenship (those of foreign ambassadors, heads of state, and military prisoners). Lots of legal scholars believe the same extends to babies of illegal aliens. There is a good chance the Supreme Court would rule in Trump's favor on the issue if current immigration law were changed. (And likewise, a good chance they'd rule against him).
My point is this. Trump is a filthy populist troll. Don't feed the trolls. No really, stop it. It's like Kansas farmer's advice: Never wrestle a pig. The pig loves it, and you'll just get muddy. Trump is going to say lots of crazy things. Just ignore him rather than descending to his level and saying crazy/dumb things back.
The closest we have to a Supreme Court decision on the matter is Plyler v. Doe, which deals with a separate issue. It's discussion of 'jurisdiction' could potentially apply to newborns.
The second closest is US v. Won Kim Ark, which (as the Wikipedia article says), many legal scholars do not think applies to illegal immigrants.