President Trump tweeted this on Sunday:
I would be willing to “shut down” government if the Democrats do not give us the votes for Border Security, which includes the Wall! Must get rid of Lottery, Catch & Release etc. and finally go to system of Immigration based on MERIT! We need great people coming into our Country!— Donald J. Trump (@realDonaldTrump) July 29, 2018
In the last short "shutdown" in January, the Democrats got the worst of public opinion, but it will be harder for Trump to blame the Democrats when he's leading the public charge for a shutdown.
A couple of days before Trump's tweet, Senate Majority Leader Mitch McConnell said that the issue would probably have to wait for a vote until after the midterm election.
Here's my take:
1) Trump really wants the wall. It's his signature issue, with another signature of his being efforts to honor campaign promises.
2) He's trying to rally his base to vote in Senate races in red states represented by Democrats up for re-election, such as in Indiana, West Virginia, and North Dakota.
3) He's conceding the House to the Democrats because the more he pushes "build the wall", the worse it is for the many vulnerable Republican congressmen in blue states like California and in the northeast.
4) He may think that it's worth going through two years of hell with Dems in control of the House because it will allow him to blame them for things not getting done, and it will give him something other than Republicans to run against in 2020.