For the first two nights of the Democratic National Convention convention, Donald Trump’s presence was hardly felt as the party struggled with its own unification. On Wednesday night, the Republican nominee starred front-and-center, as a parade of speakers delivered blistering assaults and withering critiques of his policy positions, judgment, and preparedness for the White House. “America is already great,” Obama said, rejecting Trump’s slogan and criticizing the gloomy tone at the GOP convention in Cleveland last week.