Trump will declare the situation at the Southern Border a national emergency, he will explain why a wall is necessary, and he will call upon Congress to authorize the money to build the Wall. He will warn that if Congress does not authorize the funds, that the government shutdown will continue until it does, but that he will direct the military to begin construction on the Wall.
Nancy Pelosi will respond that we are a nation of immigrants, that the Wall is immoral, that the Democrats will never fund it, that Trump's use of the army is an unconstitutional usurpation that the Democrats will challenge in federal court.
Trump will declare the situation at the Southern Border a national emergency ...
and will order the military to begin construction in exchange for opening the government, the Democrats will go to the 9th Circuit anyways, who will halt construction, and the Democrats will end up with everything they wanted.