Manafort was hired specifically to manage delegates, a job he had done before for others. He was hired because he was an expert. It’s important to remember he had been selected because he had worked as a delegate expert for some other politician(s) in the past. Wonder who they were?
I think he did it for Ford, don’t know about any others.
Manafort “joined Donald Trump’s presidential campaign team in March 2016 and served as campaign manager from June to August 2016. He was previously an adviser to the U.S. presidential campaigns of Republicans Gerald Ford, Ronald Reagan, George H. W. Bush, and Bob Dole.”
https://en.wikipedia.org/wiki/Paul_Manafort