Yes, but DJ will not bring close to as much as PP in a trade. If someone is willing to give high #1 and a starter for Johnson DO IT NOW!!!
Right and while I like DJ, right now he's not anywhere near as good as PP. You have to consider replacement value too. The Cards have been trying for years to get a #2 CB to team with PP, how easy is it going to be to get a # 1 CB to replace him?
PP is still an elite top 3 CB in the NFL IMO, right now DJ is a guy who could be an elite RB (again) but isn't playing like it. If there are teams out there willing to give up a first round pick for him, at least look into it.
I'd prefer to keep him, you don't get an elite offense by trading your best players, but this team has so many holes. You want to get to where you have multiple picks in the first 2 rounds.