A US House of Representatives panel has voted to hold attorney general William Barr in contempt of Congress amid a showdown over the Mueller report.
Democrats on the judiciary committee took the rare step after Mr Barr refused to submit an unredacted version of the special counsel's findings.
President Donald Trump has hit back by asserting executive privilege over the report, shielding it from public view.
The White House and Congress accused each other of abusing power.
Why was there a contempt vote?
The judiciary committee voted 24-16 along party lines on Wednesday to refer a contempt citation against the attorney general for a full House vote.
Democratic lawmakers put forward the measure after Mr Barr did not comply with a legal order to release the Mueller report without the redactions.
The 448-page report was released last month with parts blacked out, including information that is classified or linked to pending investigations.
The special counsel did not conclude there was a criminal conspiracy between Moscow and the Trump campaign to influence the 2016 US presidential election.
But Mr Mueller detailed 10 instances where Mr Trump possibly attempted to impede the investigation.
Democrats say they need to see the full report and its underlying evidence to investigate possible obstruction of justice by Mr Trump.
House judiciary chairman Jerrold Nadler said earlier that the Trump administration's refusal to provide the full Mueller report to Congress amounts to a "constitutional crisis".
The New York Democrat said his party had had "no choice" but to move forward with the contempt vote, "otherwise, we have a monarchy".
But Doug Collins, a leading Republican on the committee, said Democrats were acting out of anger and fear "without any valid legislative reason".
Could the attorney general be charged?
For Mr Barr to actually face the prospect of charges, the entire House - where Democrats hold a 235-197 majority over Republicans - would have to vote against him.
The measure may be largely symbolic as few expect the Department of Justice to indict its own head with criminal contempt.
However, it would send a powerful message to the White House that congressional Democrats won't retreat in an increasingly vitriolic showdown.
The last attorney general to be held in contempt of Congress was Eric Holder in 2012 during the Obama administration.
How did the White House respond?
The White House earlier on Wednesday accused Democrats of a "blatant abuse of power" and blocked access to the full Mueller report by claiming "executive privilege".
Executive privilege allows a president to keep certain materials private if disclosing them would disrupt the confidentiality of the Oval Office decision-making process.
Press Secretary Sarah Sanders said the president had taken such a step at the attorney general's request to reject "unlawful and reckless demands" by Democrats.
She added in a statement: "They didn't like the results of the [Mueller] report, and now they want a redo."
The judiciary committee chairman argued the White House was misapplying the doctrine of executive privilege.
Mr Nadler said: "This decision represents a clear escalation in the Trump administration's blanket defiance of Congress's constitutionally mandated duties."
Will Robert Mueller testify?
The House Judiciary Committee has formally requested that Mr Mueller testify, though a date has not been set.
The special counsel is still a Department of Justice employee, which means the attorney general could prevent him from testifying.
Mr Barr has previously said he would not mind Mr Mueller testifying before Congress.
Mr Trump, however, has said the special counsel should not testify, tweeting: "No redos for the Dems!"
When Mr Mueller initially handed in his report, a spokesman said he would be leaving the department "within the coming days".
If he does quit, he will become a private citizen and able to testify regardless of the department's wishes.