Why doesn't Congress simply pass a funding bill and override Trump's veto?
Doing so would be political suicide for Mitch McConnell and it would reflect very badly on any Republican Senator who votes for an override.
Why? "The Wall," the shutdown, and Trump are all extremely unpopular right now. I don't see how refusing to back the president on something so unpopular would be "suicide."
They're unpopular with the nation as a whole. But the wall and Trump are popular within the Republican base, which exerts more immediate influence on Republican politicians.
Thank you. This makes the most sense, but the wall and shutdown are so unpopular that even some of the base must be unhappy with it, and things will only get worse as the shutdown continues. But I guess they hope the more they double down on the base, the more enthusiastic/angry they will be. Sigh.