Bolton has let it be known that he will testify...But what gives him the right to dictate terms?

[gratuitous]

7. Republicans don't recognize a personal civic duty

It's up to everyone else to be a good citizen, but not Republicans. Say you're a witness to a car accident or an assault. Of course you leave your name and contact information with the police, because you're a good citizen. When the D.A. contacts you some time later, you answer all the questions, and as the trial date nears, you make arrangements to testify. That's what a good citizen does. You may even turn your witness fee check back in uncashed because you're doing your civic duty.

If you're a Republican, though, citizenship is everyone else's duty. Your duty is to get paid for doing what everyone else does freely and willingly. John Bolton isn't going to talk for nothing; he's going to need cash up front and no, you can't know what he's going to attest to ahead of time.