Oh dear God no, please don't get me wrong - I'm in NO way at all endorsing or supporting the moron who sits in the Oval Office nor the ridiculous wall policy!
Forget the person, and forget the specific policy. All I'm trying to saying is that if the Executive in a democracy gets voted in after campaigning / about a certain policy, then is it not rather undemocratic for the House to block / prevent / refuse funding for the policy?
Let's say there's a general election June 2019. The Vulture Party have some insane policies and promises in their manifesto. One of the foundation / core / headline policies during campaigning was to build a wall between England and Scotland.
The election takes place, and The Vulture Party form a minority government propped up with the DUP.
Now, with The Vulture Party in power, they put their budget together and attempt to get it through Parliament. Now at this point, Her Majesty's Most Loyal Opposition vote against it and say they'll only vote for it if the PM removes the funding request for the mighty wall. (I know that my comparison falls apart here as in theory The Vulture Party should have a majority).
If party gets voted in based on a manifesto which has a policy about building a wall, then it doesn't seem very fair for the opposition party to block it. The executive has a strong mandate to implement the policy that came straight from the electorate.
But please, do not think for a moment that I support either Trump or his ridiculous policy!