Special counsel Robert Mueller said in a rare and remarkable public statement on Wednesday his investigation could not clear President Donald Trump and that charging the President was not an option his office could consider.

In Mueller’s first public comments on the investigation since he was appointed special counsel two years ago, he emphasized that Justice Department guidelines did not allow him to charge a sitting President, and as a result, his office did not determine whether Trump had committed obstruction of justice.

“If we had had confidence that the President clearly did not commit a crime, we would have said so,” Mueller said. “We did not, however, make a determination as to whether the President did commit a crime.”

As he announced he was closing the special counsel’s office and resigning from the Justice Department, Mueller delivered a road map of how the investigation played out and the possible role that Congress could play in holding Trump accountable.

Mueller highlighted how the “Constitution requires a process other than” the criminal justice system to hold officeholders accountable, a clear signal that his obstruction investigation into Trump could be picked up by Congress.

House Judiciary Chairman Jerry Nadler, whose committee would lead impeachment proceedings, said in a statement that Congress should now respond to Mueller’s findings.

“Given that special counsel Mueller was unable to pursue criminal charges against the President, it falls to Congress to respond to the crimes, lies and other wrongdoing of President Trump – and we will do so,” Nadler said. “No one, not even the President of the United States, is above the law.”

House Democrats have been eager to have Mueller testify publicly, but Mueller’s comments made clear he does not plan to do so.

“I hope and expect this will be the only time I will speak to you in this manner,” he said.

“It’s important the office’s written work speaks for itself,” Mueller said about his report, which was delivered in March to Attorney General William Barr. “The report is my testimony.”

The Justice Department released a redacted version of the special counsel’s report last month. The report detailed numerous cases in which Trump asked his aides to take actions that would have obstructed the investigation, but stated they were unsuccessful because the aides refused his orders.

Charging Trump was “not an option” because Justice Department regulations prohibit charging a sitting president with a crime, Mueller said. His office was “bound by that policy.”

Trump has claimed ‘complete and total exoneration’

Trump, citing a letter from Barr to Congress about Mueller’s conclusions, has previously said the investigation provided a “complete and total exoneration.”

But Mueller’s report only said the investigation “did not establish that members of the Trump campaign conspired or coordinated with the Russian government,” and Mueller expressed concerns in a letter to Barr that the attorney general’s letter summarizing his findings didn’t fully capture his report, a source with knowledge of the letter has told CNN.

Trump has wavered publicly in recent weeks on the prospect of Mueller’s testimony before Congress as his administration has clashed sharply with lawmakers over demands for documents and testimony.