President Trump promised the largest tax cut in history, but as he hit the road Wednesday to promote the plan, Republicans in Congress were quietly discussing scaling back key provisions in an effort to deliver the top White House priority. There’s already talk that the cornerstone of the GOP proposal — a dramatically reduced 20% corporate tax rate that Trump has called a “red line” — may slip to 22% or 23%, those familiar with negotiations said. Trump had originally promised a 15% rate for corporations. But Republicans are running into resistance from lawmakers and lobbyists who want to preserve...