Democratic Sen. Jon Fetterman was the closest held secret of the GOP's midterm convention so far. Only President Trump, Sen. David McCormick, and a handful of senior White House aides knew beforehand that Fetterman planned to buck his own party's leadership, according to a person familiar with the matter.

Fetterman introduced McCormick, his Republican counterpart, in taped remarks praising bipartisan efforts to bolster the steel industry and condemning the left wing of the Democratic Party. It was McCormick, according to the person, who facilitated the video. The two senators had previously agreed to never campaign against one another despite their party differences. While Fetterman didn't announce he is switching parties, his cameo left some Democrats fuming at the perceived betrayal and delighted the Republicans who kept the secret.