Hillary Clinton may not have a serious opponent for the Democratic nomination — except herself.

The Clintons' unfortunate tendency to be their own worst enemy is on display, again, with reports that, as secretary of state, Hillary Clinton conducted official business solely from a personal e-mail account.

This is a problem — and not only because it presents a particularly unflattering contrast with the move by former Florida Gov. Jeb Bush to release a flood of official e-mails.

It illustrates Clinton's reflexive impulse to secrecy over transparency, a tendency no doubt bolstered by the bruising experience of her White House years, yet one that she would be well advised to resist rather than indulge.

And — not that shoe-on-the-other-foot comparisons have much power to embarrass in politics these days — but it contrasts with Democrats' howls of outrage over disclosures that operatives in the George W. Bush White House conducted official business on private e-mail accounts.

Indeed, Clinton herself was once worked up about this very issue. "We know about the secret wiretaps, the secret military tribunals, the secret White House e-mail accounts," she said back then.

So what to make of the revelation that Clinton avoided official e-mail entirely while at State? This had to be a deliberate decision. After all, the issue of the Bush e-mails was still in the news.

And, as the Washington Post's Philip Bump reports, the e-mail domain clintonemail.com that she appears to have been using was created on Jan. 13, 2009, the very day Clinton's confirmation hearings began.

To back up: The Federal Records Act requires agencies to maintain records of official business, including e-mails. The National Archives, which oversees such collection, had this to say in 2013 about the use of personal e-mail accounts:

"While agency employees should not generally use personal e-mail accounts to conduct official agency business, there may be times when agencies authorize the use of personal e-mail accounts, such as in emergency situations when federal accounts are not accessible or when an employee is initially contacted through a personal account. In these situations, agency employees must ensure that all federal records sent or received on personal e-mail systems are captured and managed in accordance with agency record-keepingng practices."

(Italics mine.)

So far, the explanation from Clintonworld about the failure to comply with this basic rule of modern archiving has been inadequate and unpersuasive.

Clinton spokesman Nick Merrill "declined to detail why she had chosen to conduct State Department business from her personal account," reported the New York Times, which broke the story. Merrill said that because Clinton was communicating with other State Department officials on their government accounts, she had "every expectation they would be retained," the Times added.

This has the distinct odor of hogwash. First, the basic rule that government business is to be transacted from government accounts doesn't have a well-we'll-capture-it-anyway exception.

Second, the government records to be retained aren't only intra-agency communications. If Clinton is e-mailing with world leaders or others about official business, the entire point of the Federal Records Act is to ensure that those communications are captured for history.

This should have been clear. Certainly, the intersection of e-mail and federal records law has been evolving. Former Secretary of State Colin Powell writes about his effort to use "the then-newfangled e-mail system" to communicate with counterparts overseas. His successor, Condoleezza Rice, rarely used e-mail to transact business but employed her government address when she did.

Nonetheless, by the time Clinton assumed office in 2009, "nobody in government understood that a high-level official would solely use a private e-mail system," said Jason R. Baron, a lawyer at Drinker Biddle & Reath and former director of litigation for the National Archives and Records Administration. If officials also used private accounts, he added, regulations in place at the time provided that "you need to transfer those e-mails to an official record-keeping system."

What is the legitimate reason for conducting official business on a personal back-channel? Why, if not for purposes of secrecy, would Clinton choose to operate that way?

That Clinton has recently turned over 55,000 pages of e-mail records in response to an overdue burst of documentary housekeeping by State does not excuse her lack of compliance while in office.

That her proto-campaign describes her activities as complying with "both the letter and spirit" of the rules would be jaw-dropping, if it weren't so sadly familiar.

Ruth Marcus' e-mail address is ruthmarcus@washpost.com. Her column is distributed by the Washington Post Writers Group.