>so why did he sign it?
What's he supposed to do when most of congress, both Rs & Ds, voted to pass it? He vetoes the bill and either it gets overridden (meaning his own party is against it), or the R's back him and they own the shutdown. That's all we would fucking hear about.
So just sign the bill to take that off the table and push the narrative that the border will stop an invasion. When that becomes clear, you'll have normies realizing that the 'no border wall' proponents are detrimental to US security. If, further, you show proof they profited off that it's pretty much over for them.
So the narrative should become that congress is a useful as tits on a bull. Politicians ain't gong to solve shit, so we'll go around them. Trump has been saying that since day 1.
Anything bad that happens on the borders, politicians now own, anything positive surfacing from increased border security, Trump's boys own. Pols probably wanted a bullshit bill to get a Trump knee jerk shutdown, but Trump pinned anything that happens on the border on them by just signing the bill and doing an end around with an NE.