In particular, because the President is the source of classification authority, the oversight functions that would normally be fulfilled by financial disclosure

In particular, because the President is the source of classification authority, the oversight functions that would normally be fulfilled by financial disclosures on forms like the SF-86 have traditionally been fulfilled by the electorate. The financial disclosures are part of the process of ensuring that people entrusted with national security information are "reliable, trustworthy, of good conduct and character, and loyal to the U.S." Candidates releasing their tax returns is a (less rigorous) process aimed at the same thing.