Last year, before Hillary Clinton's secret email system became publicly known, Congress passed a law to keep presidents from trying the same trick. If Clinton wins the White House, the law could well be put to the test.

The statute is the Presidential and Federal Records Act Amendments of 2014. It recognizes that government officials sometimes (or in Clinton's case, all the time) want to use private email accounts — in the words of the law, "non-official electronic messaging accounts" — to conduct government business. Such communications are still federal records, Congress declared, and must be preserved in accordance with existing laws requiring not just the president but all federal officials to preserve their documents.

This is what the new law says about emails:

The President, the Vice President, or a covered employee may not create or send a Presidential or Vice Presidential record using a non-official electronic message account unless the President, Vice President, or covered employee (1) copies an official electronic messaging account of the President, Vice President, or covered employee in the original creation or transmission of the Presidential record or Vice Presidential record; or (2) forwards a complete copy of the Presidential or Vice Presidential record to an official electronic messaging account of the President, Vice President, or covered employee not later than 20 days after the original creation or transmission of the Presidential or Vice Presidential record.

That's pretty clear. All presidential communications must be preserved in a timely fashion.

The next paragraph of the law stipulates that federal employees who intentionally violate the Presidential Records Act are subject to "disciplinary action" as determined by the "appropriate supervisor." Such punishments can include suspensions and cuts in pay and rank.

None of that, of course, applies to the president of the United States. As far as the chief executive is concerned, there's no enforcement mechanism in the law.

"The Presidential Records Act is set up on the notion — like all of our laws — that people are going to comply," notes a lawyer who follows these issues after service in the Justice Department in both the Reagan and George H.W. Bush administrations. "There isn't really a clear legal way to hold the president accountable for this stuff."

The Records Act gives the president entirely appropriate discretion to control the disposition of his or her records not only in the White House but for a number of years after. There are plenty of areas — personnel decisions, for example — in which a former president might not want sensitive documents released for a long time. Within limits, it is the president who makes those decisions.

But that's assuming records are kept at all in some way that federal officials have access to them. The lesson of the Clinton email affair is that Hillary Clinton is inclined to set up secret, tightly limited and carefully controlled systems that are outside the reach of federal officials. When Congress expressed an interest in examining Clinton's server, her personal attorney told lawmakers to forget about it — the whole thing, backups included, had been erased.

What would happen in an entirely plausible scenario in which Clinton did something similar in the White House? After all, a President Hillary Clinton would have far more power to set up a secretive system of communications than a Secretary of State Hillary Clinton. Who could tell her no?

No one — at least until the story became a public issue. "Ultimately, this relies on the presence of some ethical people around the president, who feel obliged to blow the whistle on wrongdoing they can't rectify internally," says Bradford Berenson, who served in the George W. Bush White House counsel's office, "plus congressional overseers (dependent upon the opposite party having one house of Congress), and finally, the press."

The problem isn't entirely new. Barack Obama is the first president to use email, but it's been around the White House for years, and an email scandal of sorts broke out in the W. Bush years, mostly having to do with the CIA leak case. A President Hillary Clinton, if she behaved in a way similar to the way she behaved as secretary of state, could create a scandal of far bigger proportions.

Ultimately, the Presidential Records Act depends on the honesty of the president. That's not Clinton's strong suit. Recent polls have shown substantial numbers of Americans do not believe she is honest and trustworthy. After the State Department experience, they would have good reason to be suspicious of her in the White House.

Don't look for this to become a big campaign issue — compliance with the Presidential Records Act is not exactly the most critical issue facing voters in 2016. But as far as Hillary Clinton is concerned, it could be a harbinger of bigger problems to come.