The House Judiciary Committee has set May 21 as the date for former White House Counsel Don McGahn to testify, although McGahn has not yet confirmed his attendance.

The committee wants McGahn to address the report by special counsel Robert Mueller, in particular, the part of the report that says that President Trump asked McGahn to fire Mueller, a request McGahn refused to carry out. Mr. Trump has indicated that he will not allow McGahn to testify before Congress because he already spent about 30 hours speaking to Mueller's investigators.

"I've had him testifying already for 30 hours and it's really — so I don't think I can let him and then tell everybody else you can't," Mr. Trump said last week in an interview with Fox News.

Get Breaking News Delivered to Your Inbox

House Judiciary Chairman Rep. Jerrold Nadler also threatened Tuesday to hold McGahn in contempt if he didn't respond to a congressional subpoena for Mueller's documents.

CBS News also confirmed last week that the White House asked McGahn to publicly state after the release of the Mueller report that Mr. Trump had not obstructed justice. A source familiar with the matter told CBS News that White House lawyer Emmet Flood made the request, which McGahn did not comply with.

"We did not perceive it as any kind of threat or something sinister," said McGahn's attorney, William Burck. "It was a request, professionally and cordially made."

In Mueller's long-awaited report on Russian interference in the 2016 election, Mueller did not make a judgment on whether Mr. Trump obstructed justice. But Attorney General William Barr and Deputy Attorney General Rod Rosenstein have cleared the president.

Mueller's report, though, described 10 instances of possible obstruction by Mr. Trump, including his order to McGahn to fire Mueller in the summer of 2017, though Mr. Trump did not bring up the request again when McGahn refused.

Mr. Trump tweeted Saturday night he never wanted to fire Mueller. "Actually, lawyer Don McGahn had a much better chance of being fired than Mueller. Never a big fan!" Mr. Trump wrote.

Democrats are also trying to get Mueller to testify, but have not yet agreed on a date for him to appear. Mr. Trump this week claimed executive privilege over Mueller's entire report and the underlying documents, after Nadler issued a subpoena for the full report, including redacted portions and supporting documents.