In another week or two McConnell will have enough GOP votes to override a veto. GOP voter turnout will crater in 2020 and Trump won’t be reelected if it becomes clear the GOP doesn’t want a wall either. So much of this PR battle is POTUS trying to hide that fact.
What the GOPe wants is a funding bill with no wall money and a executive action that will be tied up in the courts. My guess is POTUS does that since the alternative (a veto override) is much worse optics for 2020.
I don’t think Trump would let the GOP push him around like that. I think he would prefer to force them to override his veto just so the voters know exactly who is responsible for all this.