Trump is an asshat with a dismal approval rating. He is catering to his base, which is getting smaller due to the shutdown. The majority of the country doesn't want the wall.
That doesn't mean that a majority of the country doesn't want border security, just that this is a shitty way to do it. The $5B is only a small percentage of what is needed to complete it. Estimates seem to be that it will be $25B, but I have seen $70B. Maintenance costs could be $500M a year.
All for a fucking wall that can be foiled by a $266 ladder from HomeDepot.co.mx Yes, Mexico has ladder technology.
Drugs are coming through current points of entry - the wall won't help.
They arrested more suspected terrorists coming in from Canada than Mexico.
Illegal border crossings are lower than they have been for years. This isn't an emergency.
Trump just knows that this is his last stand. If he doesn't get the wall then he becomes a lame duck president and will not get a second term. He knows this and the congressional Democrats know this.
Fuck Trump.