NORMAN, Okla. — Since the 1970s, the U.S. Justice Department's stance has been that the indictment of a sitting president is unconstitutional.

It was reaffirmed in a memorandum published in 2000. The view is that an indictment and subsequent criminal prosecution would tie up the president so much, they would be unable to faithfully execute the duties unique to the office.

Rick Tepker disagrees, to an extent.

The University of Oklahoma's Floyd & Irma Calvert Chair of Law and Liberty in the College of Law said while the arrest and prosecution of a president would certainly interfere with his or her duties, an indictment would not. His is one of many voices debating this very topic, particularly following the guilty verdict and plea handed down to two former associates of President Donald Trump.

"Yes, it is possible. But I don't think it's probable," Tepker said. "First of all, no one knows the answer of does the constitution permit it or not permit it. My view is the president can be indicted, but cannot be arrested, tried or prevented form being able to serve, unless he is impeached and subsequently removed from office."

This still runs counter to claims by President Trump's legal team, particularly former New York Mayor Rudy Giuliani. They assert that a sitting president cannot even be indicted without violating the Constitution.

Tepker, whose expertise is constitutional law, assesses that it is correct that a president cannot be criminally tried unless the impeachment process is successful.

"Justice cannot proceed unless the person is removed. If anything, I think the Clinton and Nixon precedents support the idea that a president can be subpoenaed, asked to testify and can be indicted."

President Bill Clinton was subpoenaed while in office for testimony in the Monica Lewinsky case, while President Richard Nixon was subpoenaed for the White House tapes in the Watergate scandal. The effort to impeach Clinton failed in the Senate, and Nixon resigned.

When it comes to indicting a sitting president, there are very few cases to examine in U.S. history, Tepker said. While this is positive for the sake of the presidency's reputation, it does not help when attempting to settle this hotly debated piece of constitutional law.

The idea that a president cannot be indicted, Tepker said, comes from the precedent set in English law that a king could not be prevented from carrying out his duties.

"There are tons of precedents in English history that people pour over to come up with these arguments," he said. "It's plain that a king could not be indicted. But I also think it's plain that we did not intend for a president to be a king.

"It is hard to imagine how one sorts out these cataclysmic constitutional crisis without the requisite amount of historical basis. We've only had a few times in American history inside this black hole of precedence and history. Anyone who speaks confidently about it is, by definition, going off the deep end."

As for historical basis, what's going on with the Trump White House right now doesn't really compare to, say, Nixon, one that it is consistently compared with in the media, Tepker said. While there has been evidence to bring those connected to the president's campaign to court -- such as lawyer Michael Cohen and former campaign manager Paul Manafort -- anything connecting Trump to their actions or obstruction of justice is speculation at this point.

"The basic line of scandal in the Nixon case is a simpler investigative set of issues," Tepker said. "Here, it's just such a mess. It involves elements of pre-presidential sleaze, fraud and treachery, arguable treason, the emoluments clause.

"The quantity of scandals is astounding. The dimensions of the Nixon case are different than the dimensions of the Trump case. But you can find common elements and common issues through the process. Here, you're at the beginning of the process."