(CNN) President Donald Trump's Supreme Court nominee Brett Kavanaugh has raised concerns about indicting a sitting president and expressed his desire to overturn a ruling upholding the constitutionality of an independent counsel.

And in newly unearthed video reviewed by CNN, Kavanaugh also implies that he believes there's only one institution that should be allowed to investigate the conduct of a president: the United States Congress.

While the comments are consistent with Kavanaugh's long-standing legal views, they raise new questions about whether the appeals court judge believes a president can be subjected to an investigation conducted outside of Congress -- significant now that a federal investigation looms over Trump, legal experts say.

"The implication is that Congress has to take responsibility for overseeing the conduct of the president in the first instance," Kavanaugh said at a 1998 event at the Georgetown Law Center in Washington when asked about his view that a sitting president cannot be indicted. "That's the role I believe the Framers envisioned, and that's the role that makes sense if you just look at the last 20 years."

Kavanaugh then added: "It makes no sense at all to have an independent counsel looking at the conduct of the President. Now to be sure, most criminal investigations are going to involve multiple subjects, so we still need a criminal investigation ongoing. But when it comes to looking at the conduct of the President, it has to be the Congress. Congress has to get in this game and not -- stop sitting on the sidelines."

There are distinct differences between a special counsel and an independent counsel -- given that a special counsel like Robert Mueller works directly for the Justice Department under a different set of rules that governed the independent counsel. The law that established the independent counsel expired in 1999, when it was replaced by the more modest Justice Department regulation that governs special counsels.

Kavanaugh's comments from two decades ago came in the context of the work of the independent counsel Ken Starr, for whom he worked from 1994-1998, as they investigated the Clinton White House. A major question now looms over his confirmation proceedings: Whether his hostility towards independent counsels and skepticism that a sitting president can be indicted affect his views of a special counsel investigating a sitting president -- namely Mueller, who is investigating Trump and whether his 2016 campaign colluded with Russians.

And those views could be highly consequential if Kavanaugh is confirmed to the Supreme Court and later rules on any matter involving the Mueller probe, including a subpoena seeking to compel Trump's testimony.

Democrats, who have thus far not yet met with Kavanaugh , and at least one Republican plan to ask about his perspective on the issue - and he's likely to face a flurry of questions about Mueller at his confirmation hearing before the Senate Judiciary Committee, a date for which has not been set.

The 1998 comments, which have not been previously reported, are once again bound to add to speculation about whether Kavanaugh accepts the Mueller probe -- or is hostile to it.

"It's impossible to disagree with Kavanaugh that, in a perfect world, Congress would take the lead when it comes to investigating misconduct and malfeasance by the President," said Stephen Vladeck, a University of Texas law professor and CNN analyst. "But what he seems to be implying here is not only that Congress should take the lead, but that the Constitution might itself foreclose independent prosecutors like Independent Counsel Starr and Special Counsel Mueller."

The White House declined to comment about the latest video of Kavanaugh's remarks.

Helgi Walker, a partner at a Washington law firm who also worked with Kavanaugh in the George W. Bush White House and supports his nomination, said his 1998 comments are consistent with his legal view about the distinct separation of powers between the branches of government as specified in the Constitution. Kavanaugh has long embraced the "unitary executive" theory, which argues it is unconstitutional for any executive branch officer to be insulated from presidential control.

"There is nothing remarkable about this quote at all," Walker said of Kavanaugh's comments. "This is consistent with what Judge Kavanaugh has always said. ... There are major constitutional questions about an independent counsel."

In a January 2018 opinion for the federal appeals court in DC, after Mueller was appointed, Kavanaugh acknowledged a distinction between an independent counsel and special counsel. But he does not detail his view about the validity of a special counsel's investigation of a president.

"The independent counsel is, of course, distinct from the traditional special counsels who are appointed by the Attorney General for particular matters," Kavanaugh wrote. "Those special counsels ordinarily report to and are removable by the Attorney General or the Deputy Attorney General."

Asked how Kavanaugh may view a special counsel like Mueller investigating the President, Walker said, "I have no idea ... I can only look at his consistent writing about the separation-of-powers doctrine."

Vladeck said that it's "one thing" if Kavanaugh is simply opposed to independent investigations of a president on policy grounds.

"It would be a much bigger deal if, as the quote might be read to imply, he thinks the Constitution forbids them," Vladeck added. "Either way, it's hard to imagine this not being a key source of questioning at his confirmation hearing."

Democrats have vowed to make Kavanaugh's views of Mueller a focus of the confirmation proceedings, demanding he commit to recuse himself from any matter involving the Mueller probe, a proposition Republicans have dismissed. But at least one key GOP swing vote also wants to know his views on Mueller.

"It's something I'll raise with him," GOP Sen. Susan Collins of Maine, a moderate from Maine, told CNN, noting also there's a difference between a special counsel and independent counsel.

Kavanaugh has made his disdain for special prosecutors well known over the years.

In separate 1998 remarks at the Georgetown University Law Center, Kavanaugh said: "Let the President decide when to appoint a special prosecutor. ... A special prosecutor should be nominated by the President and confirmed by the Senate. Not by an isolated panel of judges. The prosecutor should be removable at will by the President."

Kavanaugh added, "In my view, Congress should clearly establish the President can be indicted only after impeachment by the House and removal by the Senate."

According to a 2016 video reported by CNN on Wednesday , Kavanaugh told a conservative group that he wanted to overturn a key decision from 1988, Morrison v. Olson, that upheld the constitutionality of the independent counsel. Doing so could potentially make it easier to dismiss Mueller because a special counsel cannot be removed without "good cause" under regulations that may withstand legal scrutiny because of the Morrison decision.

"It's been effectively overruled, but I would put the final nail in," Kavanaugh told the American Enterprise Institute in 2016 about the Morrison ruling.

The comments gained attention given Kavanaugh's previous writings expressing skepticism about whether a sitting president can be indicted.

"The country wants the President to be 'one of us' who bears the same responsibilities of citizenship that all share," Kavanaugh wrote in a 2009 Minnesota Law Review article. "But I believe that the President should be excused from some of the burdens of ordinary citizenship while serving in office."