CLEVELAND — Outside the Republican National Convention on Monday, Gawker ran into Matthew Heimbach, a podcast host for The Daily Stormer, who is encouraging delegates to write in the late George Lincoln Rockwell, founder of the American Nazi Party, for president. Donald Trump, Heimbach said, doesn’t go far enough. “He needs to become an ethno-nationalist. He needs to understand that a people is the basis of a nation,” he said. “Specifically, white people.”