Sometimes they do. Dubya abrogated the ABM treaty, although technically one of the parties (the USSR) no longer existed.
We’re going to get this deal deal and we’re going to get it a lot worse. Democrats are already lining up with their hands out and will vote for it when they get what they want.
They won’t get a Ted Cruz vote but he warned that there were worse deals. They will get enough democrat votes to dump a few billion into democrat and union coffers.