President Trump's private schedules were leaked for a second time in a week on Sunday, highlighting what appears to be an act of defiance as the White House frantically investigates who might be behind the breach.

Axios reported it obtained four more days of Trump's schedules from last week, showing the president spent nearly half his time in unstructured “Executive Time," which is time during which nothing is planned in advance.

Last Sunday, the outlet published three months' worth of the president's private itinerary.

The first leak prompted Trump’s secretary Madeleine Westerhout to complain of "a disgraceful breach of trust" in a tweet.

Acting White House chief of staff Mick Mulvaney confirmed to Fox News on Sunday that an internal hunt for the source of the leak is underway, saying they are “hoping to have a resolution” this week.

Trump took to Twitter Sunday afternoon to defend his use of “Executive Time.”

“The media was able to get my work schedule, something very easy to do, but it should have been reported as a positive, not negative. When the term Executive Time is used, I am generally working, not relaxing. In fact, I probably work more hours than almost any past President,” Trump tweeted. “The fact is, when I took over as President, our Country was a mess. Depleted Military, Endless Wars, a potential War with North Korea, V.A., High Taxes & too many Regulations, Border, Immigration & HealthCare problems, & much more. I had no choice but to work very long hours!”

The leak is the latest high-profile sign of defiance within the Trump administration. Last year an anonymous individual claiming to be a senior U.S. official wrote a New York Times op-ed criticizing Trump and detailing an insider “resistance." Trump said in September he wanted then-Attorney General Jeff Sessions to find the mysterious author of that opinion piece, calling it a matter of "national security," but there so far has been no public indication that individual was ever caught.

Should the West Wing ever narrow down the source of the latest round of leaks, there may yet be some challenges.

“When you find that person or persons, and it’s likely going to be a career staffer, you’re going to learn a lot about how hard it is to fire federal workers,” Mulvaney said.