It's easy if they are on social media everyday.
You just have to encourage them to believe whatever bullshit they already do. Compliment them. Encourage their fan clubs. Give them stories about how their opponents are lying/cheating/dening their brilliance etc etc. The more it happens, the higher their social media counts climb, the further and faster they get disconnected from reality.
It's what happened to Obama. Which is why he is in hiding unable to influence shit.