Yes he did. It was called "Operation Chaos". He urged people in open primary states to go to the polls and vote for Hillary. I think Rush realized also that a black candidate would galvanize liberals and minorities and would pose a very great threat.
Unfortunately Obama was already doing the Chicago Mafia style of cheating and intimidation against Democrat primary voters, and I wouldn't doubt that there was a lot of ballot box stuffing as well.
Obama is criminal scum, and he needs to end up in prison.