Asdrubal Chavez, chief executive of Houston-based Citgo Petroleum Corp, boarded the Venezuelan-owned firm's corporate jet in Caracas on Jan. 30, after meeting with top officials of the embattled administration of socialist President Nicolas Maduro about the latest U.S. oil sanctions. Upon landing in the Bahamas - where Chavez has worked for about a year after being denied a U.S. visa - he had received word from Houston that it would be his last trip on a company plane and that his Citgo email account had been shut off. Day-to-day control of the company had passed to Citgo's top U.S. executive,...