HOUSTON — Days after a top adviser to President Trump questioned Senator Ted Cruz’s chances of winning re-election, the Texas lawmaker casually stepped into the pinnacle of his hometown’s energy industry on Tuesday — the lobby of the Petroleum Club of Houston, on the 35th floor of a downtown skyscraper. Mr. Cruz shook hands while holding a cup of McDonald’s coffee. By the end of his remarks to the American Petroleum Institute, the audience rose for two standing ovations. It was not a campaign event, but it might as well have been: Mr. Cruz was relaxed and confident, eager to...