Bill Kristol has not given up on defeating Donald Trump.

He’s tried and failed once before to recruit an independent candidate to challenge Trump in 2016. Now, with 2020 on his mind, Kristol badly wants a Republican to primary the president. The conservative commentator has been traveling to Iowa and New Hampshire, running a campaign for a campaign, and evangelizing on behalf of a cause that’s less about policy and more, to him, about morals.

“I have a feeling,” Kristol said Wednesday at Politics & Eggs, a can’t-miss speaking engagement for White House prospects at Saint Anselm College, “that we are now entering … a turbulent era, when the character of both parties is up for grabs.”

He’s quick to note that challenges to sitting presidents had big consequences in other turbulent periods: In 1968, Eugene McCarthy and Bobby Kennedy chased President Lyndon Johnson from the race at the height of anti-Vietnam War sentiment; in 1976, Ronald Reagan nearly beat President Gerald Ford, a preview of the conservative Reagan Revolution to come; and in 1980, Ted Kennedy challenged President Jimmy Carter and helped define the liberal direction of the Democratic Party.