Joshua McCord is an agent for the President.
Officially he is a special agent with the Secret Service, charged with protecting the Chief Executive and his family. Unofficially, he seems to be the go-to guy when the President has an especially difficult job to be done.
When we first meet McCord, he is nearing the end of his career. He is getting a bit too old to leap in front of a bullet if required and he is well aware of that fact. Which is why the primary goal he has made for himself is to find a suitable replacement and to train the new guy (or gal) what it means to do what he is called upon to do.