The SCOTUS noted that the first amendment reads:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

The important bits for this case:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

Congress did make a law abridging the freedom of speech - specifically banning certain speech near an election. Therefore it got struck down.

But I guess 'progressives' don't like free speech, seeing the stunts like this they pull to mislead people.

CR