Congress as a coequal branch of government has the authority to have him arrested and jailed for failing to appear. They can hold him as long as Congress is in session. Will they? NO! Should they? Not this close to the election.
And why not? I can think of nothing more useful to this election than the promulgation of the knowledge that the man involved in Hillary Clinton's email server coverup is now in jail.
How is that a bad thing?