Retired businessman Garland Tucker III is launching a primary challenge to North Carolina Sen. Thom Tillis, one of Republicans’ most vulnerable senators in 2020.

As most primaries have been since President Donald Trump was elected, this one is already being made into a contest over loyalty to the president, which could complicate the GOP’s efforts to defend an increasingly competitive state in 2020.

Tucker, the retired chairman and CEO of Triangle Capital Corp., filed to run on Monday and an official announcement is expected in the coming days. McClatchy first reported the news.

Tucker has written two books — one about the 1924 presidential election and one about 14 conservative leaders in America — and has served on the board of the John Locke Foundation and the Civitas Institute.

The Tillis campaign immediately sought to portray Tucker’s candidacy as a threat to Trump, referring to Tucker as an “anti-Trump activist.”