Amendment IV
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
... But there has not yet been a crime
The Fourth Amendment doesn't have the word "crime" in it.
There are other reasons not to like red flag laws, but the Fourth Amendment will not offer any comfort.
