By his own admission, Donald Trump doesn’t sleep much. In his 2004 book, Think Like a Billionaire, he advised readers to not “sleep any more than you have to,” estimating that he hits the hay around 1 a.m. and wakes up at 5 a.m. to read the newspaper.

That was more than 10 years ago, and Trump’s sleep schedule hasn’t changed. “I like three hours, four hours, I toss, I turn, I beep-de-beep, I want to find out what’s going on,” he said last year in Illinois. But instead of picking up a paper, he’s now more likely to indulge a new early-morning vice—off-the-cuff tweeting. (That might be the “beep-de-beep” he’s talking about.)

Some of @RealDonaldTrump’s nocturnal submissions have made the news: His slams against Megyn Kelly (3:53 a.m.), accusations that Ted Cruz committed fraud in Iowa (1:38 a.m.), the denunciation of Alicia Machado (5:30 a.m.). They’re also a series of valuable data points about a presidential candidate’s sleep cycle—a ping that, yes, Donald Trump is awake and restless.

Using Twitter data from the past year—as well as older tweets collected by trumptwitterarchive.com—I plotted the frequency of Trump’s late-night tweeting. For the purposes of this article, I’m conservatively restricting what qualifies as “late” as a tweet posted between midnight and 3:59 a.m.; anything posted later might just be a product of Trump waking up earlier than usual. Here’s a look at the past year and a half, since Trump declared his candidacy:

On the whole, Trump’s early-morning tweetstorms seem to surge after he hits turbulence on the campaign the trail. Paging through these tweets, many of them are Trumpian “retweets”—a laudatory note from a supporter, copy-and-pasted and sometimes suffixed with a “Thank you!” from @RealDonaldTrump himself. But after bad days, they’re interspaced with dark, personal reflections.

Take the string of tweets he posted after the first Republican debate in August 2015. They start out nicely enough, highlighting a TIME web poll around 1 a.m.:

But an hour or two later, Trump begins to turn against the moderators, particularly Megyn Kelly. It begins with a “retweet” of a follower’s comment:

Twenty minutes later, Trump makes the attack himself.

This pattern repeats after other major moments in the campaign, be they good, as with Trump’s crowing tweets after the South Carolina GOP debate, or bad, as we saw more recently after he shared the stage with Hillary Clinton.

But believe it or not, Trump has actually toned down his his early-morning posts since the election began. Here’s a calendar showing the nights he tweeted late, using the same 1 a.m.-3:59 a.m. window as above. Note how often he stayed up late in 2014 and 2015, compared to this year.

Trump still consistently tweets around midnight. But his days of firing off passionate posts after 3 a.m. are far fewer, with some notable exceptions. It should be noted that most humans need sleep, and probably more of it: the Centers for Disease Control recommend between seven and eight hours. Very few people, perhaps only 1-3 percent of the U.S. population, are “short sleepers,” needing only a few hours to get by. Maybe Trump is one of them. Maybe not. A presidential campaign is grueling; perhaps it has tempered even Trump’s famed insomnia.

These insights are only possible because Trump often picks up the phone and tweets himself, instead of handing off that responsibility to an aide. (For the record, the vast majority of late-night tweets came from an Android device, believed to be his personal phone.)

A similar analysis of Hillary Clinton’s carefully managed account would likely reveal far less. I’ve written before about how it seems Trump’s Twitter presence has become increasingly staff-managed. But the wee hours of the morning, it appears his voice is still his own, unfiltered. It’s telling how he chooses to use it.