Which assumes rational government. Our government is controlled by one party and yet we are heading to a government shutdown over immigration. Rational seems far away.
That single party has the majority of both houses of Congress and also the White House, and yet cannot manage to get a majority vote in the Senate because of disagreement within their own party.
The opposing party is not threatening shutdown. A group within the majority is. Since that group within the majority party won't play ball, the majority of the majority party is hoping to garner some support from the minority party.
As it happens, some of the changes they want to make would require 60% of votes rather than just 50%+1, but they haven't yet demonstrated they can get to 50%+1, so that's irrelevant here.
