William Barr, President Donald Trump’s pick to replace ousted Attorney General Jeff Sessions, sent a letter to Deputy Attorney General Rod Rosenstein in June, criticizing the Russia probe, The Wall Street Journal reported.

The 20-page memo focused specifically on the obstruction of justice portion of special counsel Robert Mueller’s investigation. According to the WSJ’s review of the document, Barr said Trump was acting within his authority when he fired former FBI Director James Comey. Barr offered his insight as a “former official” whose “views may be useful” before calling the investigation “fatally misconceived.”

“As I understand it, his theory is premised on a novel and legally insupportable reading of the law,” Barr wrote, according to the WSJ. “Moreover, in my view, if credited by the Justice Department, it would have grave consequences far beyond the immediate confines of this case and would do lasting damage to the Presidency and to the administration of law within the Executive branch.”

Barr’s opinions on the Russia probe are of particular significance given the authority he’ll have over the investigation if confirmed. Lawmakers were already primed to grill Barr over his thoughts on the Russia probe.

Read the full WSJ report here.