Voter rolls should be verified, voter ID should be required, ink should be applied to a finger, and primaries should be closed to non-party members.
The fact that neither party really wants the system to be airtight makes me weep for my country.
Agreed. Also, as well as your prudent reforms I'd suggest a flat rule to be implemented across the country requiring congressional constituencies to be required to comply to a single standard around density and shape to prevent or at least minimise the current gerrymandering both parties practice. No more of these farcical ones that are 25 blocks long and one block wide to avoid a clump of enemy voters!