Washington (CNN) The only lawmaker to have worked on three congressional impeachment probes said Sunday that President Donald Trump's conduct involving Ukraine "is more serious" than former President Richard Nixon's Watergate scandal.

California Rep. Zoe Lofgren, a California Democrat who helped draft an article of impeachment against Nixon as a congressional staffer and served on the House Judiciary Committee during President Bill Clinton's impeachment, told CNN's Dana Bash on "State of the Union" Sunday that she agrees with House Intelligence Committee Chairman Adam Schiff that Trump's actions involving Ukraine are "far more serious" than Watergate. Congressional Democrats -- including House Speaker Nancy Pelosi and, on Sunday, Minnesota Sen. Amy Klobuchar -- have compared Trump's involvement with Ukraine to the scandal that prompted Nixon to resign in 1974 rather than be impeached.

"The president -- President Nixon's misconduct related to trying to use the levers of government to hide the Watergate burglary ... his misconduct had to do with trying to throw the election but at least it didn't involve involving other foreign nations," said Lofgren, who currently serves on the House Judiciary Committee. "If you take a look at the -- what the founding fathers were concerned about, it was the interference by foreign governments in our political system that was one of the gravest concerns. Nixon's behavior didn't fall into that range. So in that way, this conduct is more serious."

The House Democrats' impeachment investigation is centered on a whistleblower complaint alleging the President pressured Ukraine to investigate a political rival to help the President's 2020 reelection bid, while withholding security aid to Kiev. Lofgren's comments come as Congress moves toward the next phase in the proceedings against Trump, with the House Intelligence Committee expected to allow lawmakers to review its impeachment report Monday ahead of a schedule vote to approve it on Tuesday.

Asked if she would criticize Democrats for moving to impeach Trump without any Republican support -- similar to her criticism of the GOP's move to impeach Clinton in 1998 without Democratic backing -- Lofgren said, "Certainly not."

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