Stephen Miller is in the Russia investigation hot seat — the highest-ranking Trump administration official to be questioned so far.

The Russia investigation is continuing to ramp up, with special counsel Robert Mueller indifferent to repeated attacks from Donald Trump and his allies in Congress.

Mueller has now taken his investigation straight into the White House, interviewing top Trump adviser Stephen Miller, “the highest-level aide still working at the White House known to have talked to investigators,” according to a new report from CNN.

Miller was reportedly questioned about his role in Trump’s firing of FBI Director James Comey, after Comey refused to shut down the Russia investigation. Many said the firing was obstruction of justice — and Miller could be a key to that particular line of inquiry.

Miller is the only one left remaining in the Trump administration from the original group of white nationalist advisers Trump hired, including Steve Bannon and Sebastian Gorka. He has shaped many of Trump’s positions on curbing immigration, and ominously proclaimed federal judges will not “question” Trump’s authority.

Miller’s exact role in the Comey firing — and in an incident between Trump aides aboard Air Force One 36 hours beforehand — remains a mystery. But as one of Trump’s top advisers, he was intimately mixed up in the affair.

Mueller’s pursuit of Miller is especially intriguing because it — combined with the recent news that there is enough evidence to indict former National Security Adviser Michael Flynn — suggests he is aggressively following up on accusations that Trump’s dismissal of Comey just as he was investigating Trump’s ties to Russian election hacking constitutes obstruction of justice.

The Russia investigation is now inches from the Oval Office. It is clear that nothing will deflect Mueller from uncovering the truth. And when he does, so will the American people.