while his die-hard supporters are not going anywhere, there are some that voted for various reasons that are wavering on this. they think the wall needs to be built, but not at this price, and wonder why the hell it wasn't done when he had majorities in both houses and why he is doing this now when he has a democratic house, and so are becoming disillusioned with him
the thing is, he's decided to make a stand on this, and will end up just looking like this guy with a long tie and tiny hands whining and not getting anything done