In a episode of Justice League: Unlimited, Superman pretty much didn't have a liking to Shazam and they stated Shazam had joined while Superman was away.
Shazam accidentally said, it was great that Luthor was running for president, and Superman didn't really give him a chance to explain and apologize.
Just saying, Superman was kinda out of character and did give Shazam a chance, and it worked for Luthor and Waller's favor.