The Constitution of the United States lays out that the government defends us with a military, builds and maintain roads, and enforces the laws it sets. This is done through taxation. The Constitution doesn't enumerate that it can take your money and give it to someone else because they have less.

Then all they would need to do is pass a law, saying that we are taxing X to give some benefit to all citizens. Which is, in fact, correct. That is how it works, and it is perfectly legal and moral, as long as all citizens are treated equally under the new law.