Rep. Liz Cheney said Sunday that Congress is mulling whether to issue a criminal referral to the Justice Department against former President Donald Trump for “unlawfully” seeking to obstruct certification of the 2020 election.

Mrs. Cheney, Wyoming Republican, told CNN that the House select committee investigating the Jan. 6, 2021, riot at the U.S. Capitol had uncovered significant evidence that Mr. Trump and aides had acted improperly.

“It’s absolutely clear that what President Trump was dealing with, what the number of people around him were doing, that they knew it was unlawful [and] they did it anyway,” Mrs. Cheney said on “State of the Union.” “I think what we have seen is a massive, well-organized and well-planned effort that used multiple tools to try to overturn an election.”

Mrs. Cheney, in particular, said the level of planning that went into Mr. Trump’s attempt to prevent certification of the last election may have risen to the level of criminal conspiracy.

“The objective was to try to stop the count of electoral votes, to try to interfere with that official proceeding,” she said. “It’s absolutely clear that they knew what they were doing was wrong, they knew that it was unlawful and they did it anyway.”