For anyone wondering how a businessman-turned reality TV star ascended to the presidency of the United States, one journalist with years of experience covering U.S. politics says the answer is simple: Steve Bannon.

In his new book, “Devil’s Bargain: Steve Bannon, Donald Trump, and the Storming of the Presidency,” author Joshua Green argues that the former leader of the ultra-conservative Breitbart News website and Trump’s current Chief Strategist in the White House was key to securing the presidency for Trump.

Green told CTV’s Your Morning on Tuesday that, long before Trump declared his candidacy, Bannon effectively won the election for the real estate mogul by giving him the political ideas that inform his “America first” platform and by creating a network of conservative groups aimed at tearing down his Democratic opponent, Hillary Clinton.

“Bannon was the mastermind,” Green said. “He was one of the people in his ear telling him to run hard against immigration, run hard against free trade, to try and return to a kind of American isolationism that we really haven’t seen since the 1930s or 1940s.”

According to Green, Trump didn’t have a political agenda until he met Bannon.

“He’s an opportunist. He’s someone who wants to win but he doesn’t really care on what, or what venue or what policy,” Green said. “Steve Bannon is really the man in the White House with ideas.”

The book details how Bannon created the base for Trump’s support, his key role in the election, how he influences the president in the current administration and what his future plans for the country may be.

Click here to watch Joshua Green’s full interviews with CTV’s Your Morning and CTV News Channel