Ms. McGowan posted a tear-stained selfie and began her lengthy post on Twitter, “I used to be a proud Democrat,” but said that “now I know too much,” adding, “I feel really quite a sense of loss.”

“I am not a cynical person, but America goddamn,” said Ms. McGowan. “Republicans have always been painted as the bad guys, and I’ve always seen them more as a cult, but now I realize so are the democrats and the media. Macro and micro. This is deeper than a cover-up.”