What I said above about about the design of the P-38 is similar to what happened with the F-4 Phantom II and to some extent the F-14. The F-4 was design as a pure interceptor that was later pressed into the fighter/bomber role. One shortcoming with the F-4 is that it originally didn't have a gun at all so later they added guns as pods and then internally in later models after they got the message that if you're going to use it as fighter it really needs a gun. The F-14 while being designed as an interceptor as well did have some fighter elements incorporated in the design from the start such as having an internal gun.
The F-105 was design as a tactical nuclear strike aircraft and then was pressed into the fighter/bomber role with, shall we say, poor results.