Nancy Pelosi says she thinks it is possible that Donald Trump could be indicted while president as part of the special counsel Robert Mueller's investigation.

Appearing on NBC's "Today" show on Thursday, Pelosi said Department of Justice guidelines that a sitting president could not be indicted were "not conclusive."

She said it was an "open" legal discussion whether Trump could be indicted while still in office.

Rep. Nancy Pelosi has argued that the special counsel Robert Mueller could indict President Donald Trump while Trump is still in office.

Pelosi voiced the opinion in an NBC "Today" show interview broadcast Thursday, hours before she was due to be confirmed as the speaker of the House of Representatives, a position she held from 2007 to 2011.

She described Department of Justice guidelines, which say that a sitting president should not be indicted, as not "conclusive."

When asked about the guidelines by the "Today" cohost Savannah Guthrie, Pelosi said: " I do not think that that is conclusive. No I do not."

Both Pelosi and Guthrie noted that the department guidelines were not the law. Pelosi was initially reluctant to comment on whether Trump could be indicted while in office but later said it was possible.

Here is the exchange:

Guthrie: Should the special counsel honor and observe the Department of Justice guidance that states a sitting president should not be indicted?

Pelosi: Do I think that that is conclusive? No I do not.

Guthrie: So you think it's possible that special counsel Mueller could legally indict a sitting president?

Pelosi: Let's just see what Mueller does. Let's spend our time on getting results for the American people.

Guthrie: As you well know, there is longstanding DOJ guidance that states a sitting president should not be indicted. But it is not the law.

Pelosi: It is not the law. Everything indicates that a president can be indicted after he is no longer president of the United States.

Guthrie: What about a sitting president?

Pelosi: Well, a sitting president, when he is no longer president of the United States.

Guthrie: A president who is in office? Could Robert Mueller come back and say, "I am seeking an indictment"?

Pelosi: I think that that is an open discussion. That is an open discussion in terms of the law.

The US Constitution does not say whether a sitting president can be indicted while in office.

But today's Department of Justice policy holds that a sitting president cannot be indicted. Several legal experts have told Business Insider that this policy may be the only reason Trump has not been indicted already.

In December, The New York Times published an opinion piece by a former Justice Department legal expert saying that Trump technically could be indicted but that it was unlikely to happen.