You're probably thinking that old-timey racism is a thing of the past. When we look back on this law now, we're mostly shocked and disappointed by how clearly discriminatory this was. There's no way anything like this could ever be a thing again, right?

Unfortunately, you might be wrong. For a nation of immigrants like the United States, we're never far from some group panicking about another group. In fact, the exclusion of both Hispanic and Muslim immigrants has been a big topic of political conversation in recent history. (Source)

From a strict legal standpoint, it's possible. Though the Chinese Exclusion Act is gone, repealed during World War II because China was suddenly an ally against Japan, there's nothing stopping something else from going up in its place. If Congress wanted to enact a law barring immigration from, say, Mexico or Syria, there's nothing legally stopping them from doing it.

The only thing standing against the proposed Anti-Muslim law (which people have supported citing the Alien Enemies Act, a 1798 law originally enacted to keep out, and we're not kidding here, the French) is the First Amendment. While the Fourteenth won't protect non-citizens, the First will.

See, the First states that Congress can make no law about religion. It says absolutely nothing about citizens, though. So excluding Muslims from immigrating would instantly violate that, and the Supreme Court, assuming it was interpreting the Constitution strictly, would strike it down.

However, the way around this would be naming specific countries. Again, excluding Muslims, or Jews, or Zoroastrians, or Buddhists, or any other religion is already illegal. But excluding someone from specific countries?

In theory, that's just fine. In practice, of course, it's more than a little gross.