This is simply not the right vehicle for doing this in the Continuing Resolution. There’s plenty of ways to get this done without handing the Dems a propaganda win this week. It’s just a few billion dollars, do it in the regular order budget, and then let the Dems vote it down. The wall is popular and makes sense. But shutting down the government over it is bad politics.
Mick Mulvaney sure looks like a man who is out of the loop though.
Best way would appear to be for Trump to order the Army to the border to patrol until such time as the wall can be built. That way he keeps his promise and cranks up the pressure on the Dems as the costs of that operation surpass $1 billion.