They figured out that Joe is their best bet to win the presidency. He was the only “moderate” in the field. At least he tried to run as moderate.
Now he did what he was charged to do and it is becoming disposable. Yes, I doubt he will make it too much past inauguration, he may not even make it to it.
Joe was just a vehicle to get the Mattress Pilot into the White House. His usefulness is at an end.