By the second week of December 2020, the presidential election was decided and heading to a formal vote at the Electoral College. Like President Trump, the Republican Party chairwoman, Ronna McDaniel, wasn’t ready to concede.

“Every illegal vote is stealing from a valid vote, and every state that conducted their election fraudulently is stealing from states that conducted their elections fairly,” Ms. McDaniel told Sean Hannity of Fox News on Dec. 8.

At the time, key campaign aides had already told Mr. Trump that he had lost. Advisers had found no credible evidence of fraud or irregularities that could have reversed the outcome. The Electoral College would confirm Joseph R. Biden was the winner six days later.

Yet, Ms. McDaniel’s appearance on Mr. Hannity’s program was part of her concerted efforts to help Mr. Trump dispute his election loss.

Of the major figures involved in Mr. Trump’s bid to keep power, Ms. McDaniel had received relatively scant attention. She is only now facing intense scrutiny after NBC journalists revolted over their network’s decision to hire her as an on-air contributor, leading to an abrupt end to her days-long relationship with the network.

Ms. McDaniel had recently tried to downplay her role. But a review of her record shows she was, at times, closely involved in and supportive of Mr. Trump’s legal and political maneuvering ahead of the violent attempt to block Congress from certifying Mr. Biden’s victory on Jan. 6.