(AP Photo/Pablo Martinez Monsivais) From left, Senate Majority Whip John Cornyn, Senate Majority Leader Mitch McConnell, House Majority Leader Kevin McCarthy, House Speaker Paul Ryan, White House adviser Jared Kushner, Deputy National Security Adviser Dina Powell, Treasury Secretary Steven Mnuchin, and House Majority Whip Steve Scalise wait in the Roosevelt Room of the White House for a meeting with President Trump and Vice President Pence on June 6, 2017. F ormer FBI Director James Comey’s testimony may have seemed like a boon to Democrats, but it has another effect that has been little commented on: Donald Trump is now totally dependent on congressional Republicans to avoid impeachment and therefore has no choice but to be a cheerleader for their policies and to sign whatever legislation they send him. When Trump was nominated, many people accepted his own self-characterization as a disruptive force within the Republican Party. But the party itself had already moved toward more...