Donald J. Trump rolled up victories across the country on Super Tuesday, and by the end of the evening it was clear that the former president had left Nikki Haley in the delegate dust.Mr. Trump’s coast-to-coast wins — in California, North Carolina, Tennessee, Texas, Virginia and beyond — brought a new mathematical certainty to what has been the political reality for some time: Mr. Trump is barreling toward the Republican Party’s presidential nomination.But tucked inside Mr. Trump’s often dominant statewide victories, there were still signs of vulnerability. He showed some of the…