Well almost immediately after reports of airport delays came in, Trump caved. It's unclear how much the airport stuff actually played into this though since there were reports of GOP frustration the previous day. It was probably a bit of both. I'm guessing McConnell privately pushed Trump to do this.Once airports start to shut down due to a lack of TSA agents, there is going to be a ton of pressure on Trump to cave.
It'll be interesting to see what happens next. Ann Coulter is already ripping him on Twitter, but I have a hard time seeing McConnell allowing another shutdown in three weeks. I think Trump has no choice but to declare a national emergency. Congressional Republicans really don't want that, since it almost guarantees the next Democrat president will use the same tactic to circumvent Congress and enact sweeping healthcare and climate change policy.