Sanders told Mueller that her comment that "countless" FBI employees had told her they supported the President's decision was "a slip of the tongue".
She also said a second utterance - in which she said asserted that Trump and "the rest of the FBI" had lost confidence in Comey - was made "in the heat of the moment".
Mueller's report concluded that her comments were "not founded on anything".
Given that she made the erroneous statements on two separate occasions, her explanations for them raised the possibility that she not only lied, but lied in explaining why she lied.
"I hope and trust that she understands why this is a big deal and why it matters to us and to her," said Peter Baker, the veteran New York Times White House reporter.
"A press secretary's most important asset is credibility. If you don't have that, there's not much point. But we all make mistakes. The test is what you do about it to make things better."
Sanders hasn't offered an apology or a public correction. Instead, she has gone on offense.
After repeating the "heat of the moment" excuse during an interview on Good Morning America, she fired back, "I'm sorry that I wasn't a robot like the Democrat Party that went out for 2 1/2 years and repeated time and time again that there was definitely Russian collusion between the President and his campaign."
Ryan, a CNN political analyst who covers the White House for American Urban Radio Networks, was having none of that.
"She has acknowledged that she lied under oath," she said. "You can't trust her. End of story."
She added, "She's been caught in lie after lie. It's beyond spin. She speaks for the President, so it's life and death. In any other job, if someone acknowledged they lied under oath, they'd be gone. They'd be terminated."
After Ryan called for Trump to "start lopping the heads off" of discredited officials, including Sanders, Sanders' father, former Arkansas governor Mike Huckabee, called the comment "an incitement to murder" on Twitter.
He asked if the White House Correspondents' Association (WHCA) would revoke Ryan's press credential, apparently unaware that the WHCA doesn't issue press credentials.
Sanders told Fox & Friends that the comment was "a new low for the liberal media".
To some extent, Sanders' credibility is a moot point among reporters, given her increasing isolation from and limited contacts with the press.
Under Sander's tenure, formal press briefings have all but disappeared, relieving Sanders of what was, at least in previous administrations, the press secretary's primary daily responsibility.
As of Tuesday (US time), the Trump White House will set a record for the longest stretch without a briefing, 43 days. This breaks the previous record set in March (42 days), which broke the record set in January (41 days). Since the beginning of the year, Sanders has had just two briefings, fielding press questions for a mere 30 minutes or so in total.
Sanders sometimes holds Q&As with reporters on the White House driveway outside the James S. Brady Press Briefing Room. But these are both informal and irregular. She has also become well known among reporters for not responding to emails or calls to her office seeking comment.
Sanders did not reply to a request for comment for this story.
One reporter points out that Sanders can be helpful in the limited times she does engage, but not in a way that the public - or the President - sees.
Sanders still has access to the President and can be a useful source on background or off the record, said the reporter.
"She won't deny things that she knows to be true," said the reporter, who spoke on the condition of anonymity because her employer hadn't approved her speaking for publication.
"As far as I'm concerned, the Mueller report hasn't changed anything," said Olivia Nuzzi, who covers the White House for New York magazine. "Sanders never should have been relied on, and she should not be relied on now."
