Former special counsel Robert Mueller chose to break his silence and defend his investigation this weekend after weeks of contemplating doing so, in part because an inflammatory and factually incorrect White House statement attacked his prosecution of President Donald Trump’s ally Roger Stone, according to multiple sources familiar with the Mueller team.

Mueller’s Washington Post op-ed on Saturday — in which he declared Stone “rightly” remained a convicted felon — came after members of the special counsel’s team had urged him to say something. Mueller has considered publicly defending his former office and their findings on Russian interference in the 2016 election for months — especially after the Justice Department reversed his decision to prosecute former national security adviser Michael Flynn, the sources said.

Mueller decided not to speak after the Flynn reversal, according to the sources, but the attacks by the White House justifying Stone’s commutation on Friday finally pushed him to speak out and break away from his strict approach to stay above the political fray.