In Wednesday's address-Mueller's first public statement since the start of the roughly two-year investigation into Russian interference in the 2016 election-the special counsel resigned from his role at the Justice Department and reiterated the findings of his office's report. But, he said, the absence of a conclusion should not be mistaken for an exoneration of the president. "That's unconstitutional", Mueller said.
Sen. Kamala Harris, D-Calif., also called Mueller's statement an "impeachment referral", echoing Warren's phrasing.
"But what we've seen from the administration is a complete refusal to condemn a foreign power who attacked our democracy or even attempt to make the most basic steps to protect our voting systems for the future".
He said any testimony he or anyone else from the office gave would not go beyond their report.
A senior White House official told the Associated Press, "the White House was notified" on Tuesday night that Mueller might make a statement on Wednesday. Trump has called the investigation a "witch hunt". Barr released a redacted version of the report on April 18.
Representative Jerry Nadler chairs the U.S. House of Representatives Judiciary Committee.
"It later emerged that Mueller took issue with Barr's summation, writing the attorney general a letter in March in which he said that "[there] is now public confusion about critical aspects of the results of our investigation".
Jayme Closs' kidnapper sentenced to life in prison
Patterson, with close-cropped hair and dressed in an orange prison uniform, sat with his head down most of the time in court. Patterson told investigators he decided Jayme "was the girl he was going to take", before carefully plotting his next move.
Mueller, for his part, privately complained to Barr that a four-page letter the attorney general wrote summarising his main conclusions did not adequately capture the investigation's findings.
While Trump first praised Mueller after Barr's summary was released, the president has more recently returned to a recurring theme, alleging without evidence that the Mueller team was a collection of "angry Democrats", with the origins of the Russian Federation probe characterized by political bias.
Mueller's statement was expected to be relatively brief, about eight minutes, and Barr was given a heads-up about what he would say, according to people who were not authorised to provide details on the record and spoke on condition of anonymity. But, despite Trump's repeated assertions to the contrary, it did not reach a conclusion on whether Trump had obstructed justice.
As well, Mueller said it wasn't clear that the thing of value that was being offered to the Trump campaign rose to the level that made it a contravention of federal election law.
As for speaking with members of Congress, Mueller said, "the report is my testimony". The special counsel said the efforts by Russian Federation to interfere in the 2016 election deserved the Justice Department's attention, were of "paramount importance" and "deserve the attention of every American". As of now, nine of the 23 major candidates seeking the Democratic presidential nomination have called for an impeachment inquiry.