Ex-Attorney General William Barr's scathing critique of a major court victory for Donald Trump in the Mar-a-Lago classified documents drama is escalating the scrutiny of the judge who put the brakes on the investigation.

Barr was once seen as a facilitator of the then-President's penchant for tearing at the limits of presidential power. But since Trump's refusal to accept his defeat to President Joe Biden in 2020, Barr has emerged as one of his most acerbic and significant critics. He, for instance, infuriated Trump by publicly declaring there was no significant electoral fraud. And his video testimony has emerged as one of the key weapons in the televised hearings run by the House select committee investigating the US Capitol insurrection.

On Tuesday, Barr took aim at a decision by Trump-appointed Judge Aileen Cannon to grant Trump's request for a "special master" to vet for executive and legal privilege issues the material taken from his home in last month's FBI search.