Jeff Sessions spoke on the importance of prosecuting Bill Clinton for perjury during a television interview in 1999.
A younger version of the now Attorney General said he was concerned about a president appearing to lie “under oath” and that “no one is above the law”.
The leading Republican figure is under increasing pressure from the Democratic opposition to resign after he allegedly outright lied to the Senate about two conversations with the Russian ambassador.
“I am concerned about a president, under oath, being alleged to have committed perjury,” said Mr Sessions, speaking to C-Span.
“There are serious allegations that that occurred. In America, in the Supreme Court, the American people believe no one is above the law. The president has gotten himself into this fix that is very serious.”
The Senate were imminently due to vote on two charges of perjury and obstruction of justice against Mr Clinton, which nearly saw the Democrat impeached.
The 42nd US President – the husband of Hillary – was facing unprecedented pressure to resign over his sexual relations with White House intern Monica Lewinsky.
He famously said “I did not have sexual relations with that woman” in a press conference and repeated the statement under oath in the Paula Jones sexual harassment case.
A Washington Post article this week revealed Mr Sessions – an early advocate of Mr Trump’s during his wild-card presidential race – failed to disclose to the Senate in January his two conversations with Sergey Kislyak.
Democrat leader in the House of Representatives Nancy Pelosi said he “must resign”.
