Special counsel Robert Mueller subpoenaed Steve Bannon, President Donald Trump’s former chief strategist and the former executive chairman of Breitbart, last week to testify before a grand jury amid a probe into Russia's efforts to interfere in the 2016 presidential election, the New York Times reported Tuesday.

What happened?

According to the Times, the grand jury subpoena “could be a negotiating tactic” on Mueller’s part in an effort to push Bannon to agree to undergo questioning by investigators “in the less formal setting of the special counsel’s offices.”

The move marked the first time Mueller has been known to use a grand jury subpoena in the course of his investigation into Trump and his associates’ ties with Russia, the Times noted.

The subpoena likely indicates that Bannon “is not personally the focus of the investigation,” the report added, because “Justice Department rules allow prosecutors to subpoena to the targets of investigations only in rare circumstances.”

The subpoena comes shortly after Bannon was quoted in a new book, “Fire and Fury: Inside the Trump White House,” criticizing Trump and calling Donald Trump Jr.’s 2016 meeting with Russians in Trump Tower “treasonous.”

Soon after the book’s publication, Bannon was ousted from his role at Breitbart and Trump mocked him on Twitter as “Sloppy Steve.”

Michael Wolff is a total loser who made up stories in order to sell this really boring and untruthful book. He used Sloppy Steve Bannon, who cried when he got fired and begged for his job. Now Sloppy Steve has been dumped like a dog by almost everyone. Too bad! https://t.co/mEeUhk5ZV9

— Donald J. Trump (@realDonaldTrump) January 6, 2018

The Mercer Family recently dumped the leaker known as Sloppy Steve Bannon. Smart!

— Donald J. Trump (@realDonaldTrump) January 5, 2018

Bannon later called Trump a “great man” and noted his unwavering support of the president on Sirius XM’s Breitbart News Tonight.

According to The Hill, Bannon testified before the House Intelligence Committee Tuesday in a closed setting amid that panel’s ongoing investigation into Russian efforts to influence the election.