A document that confirms people's rights

Lately I've been reading the Constitution. It's a short document -- scarcely 7,000 words.

I can't find any place in the Constitution making a distinction between citizens and noncitizens, except in the right to vote. This is strange, because our government says that noncitizens are not protected by the Constitution.

In fact, there are very few mentions of "citizens" in the Constitution: Article Two says the president must be a "natural born" citizen; the Fourteenth Amendment says "All persons born or naturalized in the United States . . . . are citizens . . . ." The Fifteenth says "The rights of citizens of the United States to vote shall not be abridged . . . on account of race. . . ." The poll-tax amendment and the Nineteenth Amendment, which recognized women's right to vote, refer to citizens.

They are also mentioned in parts of Article III and in the Eleventh Amendment that deal with civil law suits between citizens of different states. "Noncitizen" is never mentioned.