Late Monday night, the New York Times’ Michael Schmidt reported that Hillary Clinton, when she was secretary of state, only used a personal email address for conducting official business. It’s just the latest in a string of negative stories that have put Clinton on the defensive—and should make Democrats extremely concerned about her uncontested path to the nomination.

The Times claims that during her time at the State Department, Clinton broke federal regulations about email use. “Her aides took no actions to have her personal emails preserved on department servers at the time, as required by the Federal Records Act,” Schmidt wrote. That may not be precisely true: The Daily Beast's Michael Tomasky discovered that the Federal Records Act only required Clinton to preserve copies of her emails, which Clinton appears to have done. It wasn't until October 2014—a year and a half after Clinton left office—that the State Department finally issued specific instructions for employee record management.

Still, it's a serious problem when government officials conduct business with personal email accounts because any messages sent and received are not archived on government servers. Those emails would not surface in Freedom of Information Act (FOIA) requests and subpoenas, creating a dangerous lack of transparency. That's why, also in October 2014, the State Department asked all former secretaries since Madeleine Albright to turn over any records from their time in office. “Mrs. Clinton’s advisers reviewed tens of thousands of pages of her personal emails and decided which ones to turn over to the State Department,” Schmidt writes. “All told, 55,000 pages of emails were given to the department.”

The Times doesn't say why Clinton didn't turn over all emails. If she and her advisers selectively chose which emails to hand over, we need to at least know the selection process. Otherwise, who knows what she left out?

The Clinton camp adamantly denies that it’s trying to hide anything. "Like Secretaries of State before her, she used her own email account when engaging with any Department officials,” her spokesman, Nick Merrill said. “For government business, she emailed them on their Department accounts, with every expectation they would be retained.” Hillary had every expectation, they say, that all of her communications from her time at the State Department would become public.