The question: are the tweeters using Twitter as a tool for political speech? If so, they rock. More power to them. Get out of their way.
Or are they using Twitter as a political hack-job tool, spewing out purposeful disinformation just to muddy the waters? More to the point, are they being paid by some political entity to do this? Is there damage to Corbett's life being caused by these purposeful lies?
You have maximum freedom of speech for political purposes. But if you have malice towards a person for political reasons, and are saying things you know to be inaccurate in order to hurt them, and you have hurt them in some way (perhaps instigating an investigation you know to be spurious) you've crossed the line and should be subject to civil action from the person you are purposely harming. That's not a criminal thing, but a civil thing.
EDIT: So yes, as a matter of free speech I have the right to make a bunch of things up and call you a pedophile and convicted felon on Twitter the day you apply for the job as CPA at a daycare, but if you lose the job because of it you have the right to make me pay for that damage that I purposely caused. This is no different than the freedom to have a gun doesn't give you the freedom to go around shooting people. (key concept: real measurable harm is done in a purposeful manner)