No, it's not a law, but it's become expected.
It's going to be a law. Or 50 laws, if the states require it to be on their ballot.
And the reason is going to be Trump.
I've had a vlearance since 1980, and attended one or another version of annual security training at least 60 times. Over time, you can see that someone gets caught violating or trying to violate national security, they overhaul the security programs and screening processes, and write new laws.
For example, when John Walker was selling secrets to the Soviets, he was also the guy in charge of performing his own background investigation. No one had ever imagined that THE security officer might be the security risk. Due to him, the process is more complicated and stringent. Several processes are more complicated now, thanks to the holes he revealed.
You could probably footnote every line in the security manual, every requirement, with an associated arrest, even if it did not end up in a conviction. We just realized, "Hey, no one ever asked why the midshift guy on the Encoder kept bringing an expensive camera into the Top Secret vault," and put a big No Recording Devices!!! policy in place.
So, even after Nixon, no one imagined anyone rising to the office while being so horribly compromised as Trump may be. Even if he is innocent, and prevails in court, or gets pardoned, there will be adjustments to the process. If nothing happens in the end, we've still been shocked to note what could have happened, and something will be put in place to protect against the possibility.
Things like
Release X years of taxes.
Declare sum of all debts, and identify debtors over Y dollars, and all foreign debts.
Diagram the branches of government and use the drawing to describe the life cycle of legislation. Crayons acceptable. No Sharpies.
Submit a list showing you know of at least fifty government positions you need to fill. Agencies and offices are preferred, though we will accept "the guy who runs the spies" or "the guy who runs the Navy."
