WATCH: Clinton prosecutor Ken Starr explains why Trump can be indicted -- but it would be 'hell'

In a lengthy interview with MSNBC's Ari Melber, Clinton-era independent counsel Ken Starr explained why sitting presidents can be indicted -- whether they be Bill Clinton or Donald Trump.

"There's no question" Trump lied about his personal life, Starr explained to the MSNBC host.

Though the process of impeachment is "hell," lawmakers have a duty to hold those in power accountable, the independent counsel said.

Melber pointed out that during Starr's time as independent counsel, he solicited a legal opinion that found that sitting presidents can be indicted with "the right evidence" -- an opinion he said holds as much water now as it did when it was first written.

"The Justice Department has a different view and has had a different view for almost half a century," he said. "These are very impressive legal documents with very thorough analysis -- I just happen to disagree with them."

In the Clinton v. Jones case -- one of the cases in which the former president was accused in a civil suit of sexual assault -- the president asserted that he should be "immune" from such a suit because of his office, Starr explained.

"The Supreme Court, unanimously, said 'No, Mr. President,'" Starr noted. When Clinton asked for merely a "time out," the court again denied him.

"The public interest and the enforcement of criminal law, I believe, is even higher," the former independent counsel concluded.

Watch below: