As mentioned, any background type of checks usually will require a release of information by the party being investigated and no warrant necessary.
My opinion is that everything against a US citizen by any US related government entity should 100 percent require a warrant with good cause terrorism or not!
Not hard to get a warrant if have good reason for it.
The US was founded by certain principles of freedoms, rights, liberties that everyone has and the constitutional was ratified by the states to be a protector of those rights, freedoms and liberties, which should trump all else, with the exception if violating others same rights, this should be the litmus test to all US laws, and why I feel more than not many federal laws and many state laws are actually unconstitutional. Just because a bunch of idiots who we hire to do a job thinks is good idea to pass a law does not mean it is right. We need term limits to congressional members and I think it is time to revoke the lifetime membership of supreme court justices, so the incompetent idiots there can be ousted also.We keep heading down a dangerous road giving up more freedoms for the sake of some other justification and one day we will no longer be able to write comments like these as will be an act of terrorism too!
Only thing US government should be doing protection of overall rights , defense of our nations, and other more national strategic issues like national disasters that would be too over bearing for other lower government entities to bear.