Former special counsel Robert Mueller decided he could not indict President Donald Trump while he is in office, but that is not the only mechanism for legal accountability.

Former Obama administration acting Solicitor General Neal Katyal explained to MSNBC anchor Lawrence O'Donnell on Thursday how there is another option.

"Last night a former Watergate assistant special prosecutor, Jill Wine-Banks, made a point about indicting a president that had not occurred to me," O'Donnell noted, introducing a clip.

"The evidence of all the elements of the crime has been established and were he not protected by the Office of Legal Counsel -- an opinion by the way that I think is flawed constitutionally and legally -- I think it’s incorrect. It’s time for someone to challenge it or change it. It may take a state prosecutor indicting the president to take it to the Supreme Court for a decision and whether you can cover up your own crime and get away with it," she noted.

President Donald Trump can be indicted right now, a former top Republican prosecutor explained to MSNBC's Lawrence O'Donnell on Thursday.

The host of "The Last Word" interviewed Bill Weld, the former Republican governor of Massachuttes who is currently challenging the sitting president for the 2020 GOP nomination.

Prior to his career in elected office, Weld was a top federal prosecutor.

In 1981, Weld was nominated by Ronald Reagan to be the United States Attorney for Massachuttes. After receiving positive media coverage for his anti-corruption court victories, in 1986 Reagan promoted Weld to head the Criminal Division of the Department of Justice.

It was almost a throwaway moment, but under questioning by Florida Democrat Rep. Val Demings, former Special Counsel Robert Mueller let slip a new admission in his congressional testimony Wednesday with the potential to alter the terrain of the impeachment debate.

The Florida lawmaker pressed the ex-Marine on the president’s sworn written answers to questions provided by the special counsel, given in lieu of a formal interview, which Donald Trump refused.

“Isn’t it fair to say that the president’s written answers were not only inadequate and incomplete — because he didn’t answer many of your questions — but where he did that his answers showed he wasn’t always being truthful?” Demings asked Mueller in the hearing.