The bad news is that many states do not require voting systems that can be audited by immutable paper. If a touchscreen voting machine was hacked, and if there is no voter verified audit trail, then an audit won't prove much.
The good news is that some of the important states in the 2016 election DO require paper or a paper trail I don't vouch for the website ballotpedia DOT org/Voting_methods_and_equipment_by_state, but it, at least, purports to show the states that have auditable results.
Among the states listed on the ballotpedia site are Wisconsin (must have paper trail), Pennsylvania (does NOT require paper trail), Florida (does NOT require paper trail), Michigan (requires paper ballot).
It's a whole other question why some states allow voting systems without paper audit trails. But, why not audit the states that do have paper audit trails? What's the harm?
Again, I don't vouch for the accuracy of the ballotpedia DOT org site. The data is generally consistent with the VerifiedVoting DOT org website which shows Florida and Pennsylvania do not require a paper audit trail.