I blame 90% of our failure to follow the Constitution on the 17th Amendment. The Framers considered and rightly rejected popularly elected senators; the 17th opened the door to progressive government. All good things are impossible without repeal of the 17A.
Ergo, we must have a COS.
Congress will NEVER author an amendment to repeal the 17th.
OTOH, states themselves are potentially VERY motivated to repeal it. Even leftest states like here in MA, sending leftist delegates, could be swayed, if they are ensconced in state politics and excluded from national up to now.