The only other explanation than the one below is that Trump isn't really serious about The Wall and never has been, and is only interested in how he can play the politics of The Wall.
Opposition to the wall within Trump’s own administration has prevented progress on this issue, which is wildly popular with the GOP’s conservative base and is the consequence of the president surrounding himself with establishment advisers who have worked to thwart his populist agenda from within. For example, after being briefed on the concept of selling USDA commercial paper to pay for border security, Agriculture Secretary Sonny Perdue’s then-Chief of Staff Heidi Green shot down the idea by curtly stating, “The secretary does not want the wall.”
