Nah, just a comic relief on Ep. I. Personally, I'm not even that bothered with him, he isn't funny but Ep. I was actually pretty good unlike most people like to claim.

He was a bit stupid, so people complained and Lucas just got mad and put him as a senator to piss people off.

That's a very old theory, an amusing one though, and it is true that it's his fault the Republic fell, but he's not the big mastermind.

Palpatine is, and it would take away from Palpatine's character if it was otherwise. That's why I hope Disney and the new writers are sensible and they don't make Snoke some kind of string pulling uber-baddie because Palpatine is already supposed to be just that. I hope there's some sort of relation.

Anyway if Lucas really ever did enjoy the idea of Jar Jar being a Sith, it was probably scrapped early on, either due to the character's bad reception or in favor of Palpatine's character. Now Jar Jar's just some clown.

I think that was the original plan but due for the backlash they changed the direction.
He would be the one we would least expect.