President Donald Trump says he is not considering firing special counsel Robert Mueller, but he’s plenty upset about the way the Russia probe investigator obtained and is using thousands of emails sent and received by senior Trump transition officials.

The president says of the emails, “I can’t imagine there’s anything on ’em, frankly. Because, as we said, there’s no collusion” with Russia during last year’s campaign. But he said the way Mueller got them was “not looking good; it’s quite sad.”

Trump was asked about the emails Sunday after the disclosure that Mueller’s team had obtained them from the General Services Administration, a federal agency that stored the material, rather than requesting them from Trump’s presidential transition organization.

The GSA improperly provided the records, asserted Kory Langhofer, general counsel of Trump’s still-existing transition group, Trump for America. Mueller’s team has been “actively using” the emails in its investigation, Langhofer said.

Trump himself has been harshly critical of Mueller’s probe of Russian activities during the 2016 campaign. But when asked if he was planning to fire the former FBI director, Trump said, “I’m not.”

The emails in question were provided to Mueller’s team by the GSA in September in response to requests from the FBI, but the transition team didn’t learn about it until last week, Langhofer said in a letter sent to the Republican heads of two congressional committees, the House Oversight and Senate Homeland Security panels. A copy of the letter was obtained by the AP.

Langhofer said the transition organization considers the documents private and privileged — and not government property.

The tens of thousands of emails pertain to 13 senior Trump transition officials. Some of the emails include national security discussions about possible administration international aims as well as candid assessments of candidates for top government posts, according to people familiar with the transition. They spoke to The Associated Press on condition of anonymity because of the records’ sensitivity.

Among the officials who used the accounts was former National Security Adviser Michael Flynn, who pleaded guilty to making false statements to FBI agents in January and is cooperating with Mueller’s investigation. Trump fired Flynn in February. The White House says that was for misleading senior administration officials about his contacts with Russia’s ambassador to the U.S.

Still, it’s unclear how broadly revelatory the emails will be for Mueller. Several high-level Trump advisers sometimes used other email accounts, including their campaign accounts, to communicate about transition issues between Election Day and the inauguration.

Flynn attorney Robert Kelner declined to comment. Jay Sekulow, an attorney on Trump’s personal legal team, referred questions to the transition group. Spokespeople for GSA didn’t respond to AP’s emailed requests for comment.

The special counsel’s office also obtained at least one iPad as well as laptops and cellphones that were used by the transition, but prosecutors have assured the transition that investigators have not pulled emails or other data from those devices, Langhofer said.

He said that a GSA official appointed by Trump in May had assured the transition in June that any request for records from Mueller’s office would be referred to the transition’s attorneys. According to Langhofer, the assurance was made by then-GSA General Counsel Richard Beckler, who was hospitalized in August and has since died.

But another GSA official present for the conversation told BuzzFeed News that there was nothing improper about the disclosure of the emails to Mueller’s team. The GSA has provided office space and other aid to presidential transitions in recent years and typically houses electronic transition records in its computer system.

GSA Deputy Counsel Lenny Loewentritt, whom Langhofer blames along with other GSA career staff for providing the transition documents to the FBI, told BuzzFeed that Beckler didn’t make a commitment that requests from law enforcement for materials would be routed through transition lawyers.

Transition officials signed agreements that warn them that materials kept on the government servers are subject to monitoring and auditing, Loewentritt told BuzzFeed, and there’s no expectation of privacy.

Mueller’s spokesman, Peter Carr, said the special counsel’s office has followed the law when it has obtained documents during its investigation.

“When we have obtained emails in the course of our ongoing criminal investigation, we have secured either the account owner’s consent or appropriate criminal process,” Carr said.

In a statement, Rep. Elijah Cummings of Maryland, the ranking Democrat on the House Oversight and Government Reform committee, dismissed the transition’s arguments that GSA shouldn’t have turned over the records.

The media site Axios first reported on the transfer of the emails to Mueller’s team.