Trump and his allies benefit if they're able to successfully make this a dichotomous outcome: Either they colluded with Russia or they did nothing wrong.
Only simple people believe life happens in black and white, however. There are a lot of different shades and nuances to reality.
Come to think of it, the way Trump pitches a lot of his political ideas are black and white, too. "Build that wall or crime rules all," "Repeal the ACA or you get horrible socialized medicine," "Tear children away from their families and terrorize them or they'll all just keep coming." "No oversight can be done on me or it's presidential harassment by angry Democrats." I could keep going.
If you ever wonder why, refer back to the bit about simple people.