If Trump keeps insisting on a wall, will he face a Republican primary challenger in 2020?
Can't imagine the Republicans are feeling comfortable watching Trump keeping the government closed over an issue most Americans oppose. At the moment while Trump is unpopular with Americans overall he's still popular with Republicans.
But that could easily change if they think he is boxing himself into a corner that will guarantee a loss in 2020.
So if he keeps this up and the impact of the shutdown starts getting real (impacting tax returns, air travel, etc) I think there will be increasing pressure on the GOP to run somebody else for President in 2020