A few years ago, not long after Jeanine Pirro paid a visit to Donald J. Trump at his Trump Tower office, a box arrived at her home in Rye, N.Y.

Inside was a gift: a selection of shoes from the latest Ivanka Trump footwear collection.

Ms. Pirro, the prosecutor-turned-politician-turned-television personality who hosts a weekend show on Fox News, has been friends with Mr. Trump for decades, their careers forged in New York’s tabloid caldron. But these days their relationship is playing out on a bigger stage.

Ms. Pirro has lately emerged as a force in a right-wing media effort to undermine the special counsel, Robert S. Mueller III, who is leading the investigation into Russian meddling in the 2016 presidential election. Like other pro-Trump commentators, Ms. Pirro has called for Mr. Mueller to be fired. But she has gone further, saying on the air that “individuals” in the F.B.I. and the Justice Department “need to be taken out in cuffs.”

In a fiery monologue on Dec. 16, she told her viewers: “There is a core group of arrogant, corrupt and lawless individuals that felt that they, and not we, should decide a presidential election. And when they failed, they conspired to create the false narrative to not just muddy our choice for president but to bring down his presidency and his family as well.”