Not an American Constitutional law expert, or an American but if it was completely constitutional wouldn't it have been addressed in the last 20 years?
Both sides of the aisle have held power in America in those 20 years.
In the US, the law is heavily tilted towards inaction, by design. To pass legislation you need 50%+1 of the House and 60% of the Senate and the Presidency, and after being passed it can still be challenged judicially. Any one of those can block legislation. It's actually quite rare for a party to "hold power" -- and even when it does, it would take a unanimous desire with in the party to wield it.
A notion can have very widespread support and still not pass, or get much serious work done. (It's common for the party in power to bottle something up in a committee without giving it a full hearing.) So lack of action isn't evidence one way or the other. It just means it's nearly impossible to do anything via legislation.
Unfortunately, there is so much that needs to be addressed but has not and will not in the foreseeable future unless something drastic changes.
To the comment below that is "dead" you are completely correct IMO. HN has too many gov't lurkers here manipulating votes. Most dead comments are gold.
I'm not sure what unconstitutional means here. The department is not named in the constitution, but then neither were the overwhelming majority of such. (You could say, "that ship has sailed" once the Department of the Navy was created.) It embraces quite a few agencies that go way back, including the Coast Guard, and the customs component of ICE.
A notion can have very widespread support and still not pass, or get much serious work done. (It's common for the party in power to bottle something up in a committee without giving it a full hearing.) So lack of action isn't evidence one way or the other. It just means it's nearly impossible to do anything via legislation.