WASHINGTON — A powerful House committee now led by Democrats is opening an investigation into how security clearances have been handled in President Donald Trump’s White House and 2016 presidential transition. The inquiry by the House Oversight and Reform Committee, announcedWednesday, takes direct aim at some of those closest to the president over the past two years, including former national security adviser Michael Flynn, Trump son-in-law and senior adviser Jared Kushner and former White House aide Rob Porter. The review also sets up one of the first potential fights between a Democrat-led House committee and a White House bracing for a number of investigations in the wake of last year’s midterm elections that eroded GOP control in Washington. Rep.