WASHINGTON — President Donald Trump’s tax reform plan came under new criticism on Tuesday from two towering Wall Street figures, including billionaire investor Warren Buffett, who called into question a Republican drive to slash the U.S. corporate rate.With the White House and top Republicans in Congress already on the defensive over claims the plan would not cut taxes for many middle-class Americans, Buffett and BlackRock Inc Chief Executive Larry Fink suggested in separate interviews that the corporate rate may not have to be cut as deeply as proposed.“We have a lot of businesses...