It’s not the diagnosis that gets you, to paraphrase a former U.S. president, but the cover-up.

This weekend’s revelation that Hillary Clinton has pneumonia helps explain quite a bit. It explains her persistent cough, and it explains why she had to leave a September 11 commemoration on Sunday. For weeks, there has been fevered (sorry) speculation about Clinton’s health, and now it turns out that there’s a fairly straightforward, and antibiotic-treatable, explanation.

So why didn’t her campaign say so from the start?

Even more confounding, the acknowledgment of the pneumonia diagnosis came after hours of changing stories. Last week, she was joking in Cleveland that she was “allergic” to Trump. Then, on Sunday, Clinton got lightheaded at the 9/11 ceremony in New York and had to leave. A campaign spokesman said, “During the ceremony, she felt overheated so departed to go to her daughter’s apartment, and is feeling much better.”

But attendee video showed Clinton stumbling as she was about to get into a van to carry her away. She went to her daughter Chelsea’s apartment in the city, then emerged two hours later and told the press, “I’m feeling great. It’s a beautiful day in New York.” It was only in the late afternoon that the Clinton campaign circulated a statement from Dr. Lisa Bardack, her physician, saying that she had on Friday diagnosed Clinton with pneumonia and prescribed antibiotics and rest.