MILWAUKEE — When the Republicans put the final gavel to the wreckage of their convention in Cleveland eight years ago, they were in a state of nuclear meltdown.Yes, they had a nominee in reality television star Donald Trump. But the party itself was a collection of warring factions that agreed on little by way of principles, beyond their collective desire to keep Hillary Clinton out of the White House. Strategist David Urban, who helped organize the 2016 convention for Trump, recalls that the floor of Quicken Loans Arena felt like “enemy territory.” Tensions were thick between Trump’s campaign and the...