Williamson simply presupposes that there is a coherent Trump program to sign up for, not to mention that there was a coherent Obama program, neither of which is true. Lots of Republicans have "made peace" with Social Security, but that doesn't mean they have become New Deal ideologues. Williamson ignores their political pragmatism, and Trump's.
The essay is otherwise interesting. He might have added Reagan to his so-called new nationalist "Roosevelt-Obama-Trump model", but not wanting to inflame too much is understandable given his recent history:
"Conservatives have a conflicted view of government. Many who revile FDR as the root of all welfare-statist evil revere Ronald Reagan, who insisted all his life that he was an FDR Democrat whose former party had simply gone insane."
Yes, Reagan was confused. Hence his movement, and Williamson.