This is indeed troubling. The White House/Sanders already stated that there would be a State of the Union on Tuesday. Trump fired back at Pelosi. Something has happened as to why he caved. He had several options to move forward with the SOTU just as he had options to fight this battle long ago. A couple of things;
I kept waiting for Mitch to extend an invitation to give the SOTU and none was given.
There was mention of the Gang of 20 working behind the scenes and then there was mention of Mitch and Chuckie striking a deal.
SCOTUS threw Trump a blow and refused to take up DACA, so that eliminated Trumps bargaining chip.
The DEMS played dirty refusing to pay the federal workers.
I highly doubt that Nancy and the DEMS are going to give him his money; so he's back to either caving to the agreements that Congress has come up with, or he declares a national emergency.