The chairman of the House Oversight and Reform Committee is starting an investigation into the handling of security clearances by President Donald Trump's White House and 2016 presidential transition.Democratic Rep. Elijah Cummings of Maryland says the investigation is in response to what he calls "grave breaches of national security" involving former national security adviser Michael Flynn and others. Flynn kept his clearance even after the White House learned he'd lied to the FBI about his conversations with Russia's ambassador. Flynn later pleaded guilty to a felony. He's awaiting sentencing. The investigation also is seeking information about former White House aide Rob Porter. He had high-level access with an interim security clearance even though the FBI told the White House about past allegations of domestic violence involving Porter.