I read that whole tweet as wishful, not serious. Bill's national security leaning: Sherill (NJ) is Air Force veteran and centrist and Spanberger(VA) is ex CIA and centrist. Each is considering gubernatorial run in her state. Spanberger isn't running for reelection to focus and Sherill hasn't declared.

This ticket throws nothing to liberals but has general election positive. No name recognition which is why I think it's part of the joke of the tweet.