Paul D. Ryan unanimously won the nomination of his House Republican colleagues Tuesday to continue as speaker and serve as the chief legislative partner to President-elect Donald Trump. “Welcome to the dawn of a new unified Republican government,” he told reporters ahead of Tuesday’s vote. Ryan must now win a floor vote in January of all 435 House members. If about two dozen Republicans were to withhold their support, his election would be thrown in doubt. Several Republicans made clear this week that although Trump’s victory may have eased the internal party tensions that threatened Ryan’s speakership before the election,...