WATCH: Nancy Pelosi believes Trump could be indicted by Mueller -- even if Justice Dept. says no

Soon-to-be House Speaker Nancy Pelosi disagrees with the Department of Justice guidance that says a sitting president cannot be indicted.

The California Democrat, who will become House speaker Thursday afternoon, told NBC's "Today" show that special counsel Robert Mueller was not obligated to honor that guidance and could ask a grand jury to indict President Donald Trump.

"I do not think that that is conclusive," Pelosi told NBC's Savannah Guthrie. "No, I do not."

The Justice Department issued guidelines in October 2000 holding that "the indictment or criminal prosecution of a sitting President would unconstitutionally undermine the capacity of the executive branch to perform its constitutionally assigned functions."

But Pelosi said that does not rule out the possibility that Trump could be indicted as part of the sprawling probes against him, his family, his presidential campaign and his business.

“I think that that is an open discussion," she said. "I think that is an open discussion in terms of the law."

The top-ranking House Democrat said she would not rule out impeachment proceedings, but she would wait until Mueller presented his findings in the Russia investigation.

“We have to wait and see what happens with the Mueller report," Pelosi said. "We shouldn’t be impeaching for a political reason, and we shouldn’t avoid impeachment for a political reason.”