The phrase "populist wave shtick" is unique to this article of The Guardian. Google search returns with only 3 hits, all of them referring back to the article. Does "shtick" in this context mean "a humor that tends to manipulate"?
The definition for shtick is: the type of humour typical of a comedian (= person whose job is to make people laugh). (Cambridge Dictionary)
It didn’t happen. Emmanuel Macron defeated Marine Le Pen. And Bannon himself was out of the White House within eight months. The New York Times claimed that Rupert Murdoch had persuaded Trump to fire him. I suspect it was as much about a Time magazine cover: a photo of Bannon under the headline “The Great Manipulator”. And Trump never had much time for Bannon’s populist wave shtick, implying as it did that Trump’s election was a matter of historic inevitability. In Trump’s mind, he wasn’t swept along in the wave, he was the wave.