In 1933 he built an oil refinery in
Hamburg, Germany, and developed business interests for a short time in England and somewhat longer in Germany. He served as the principal negotiator of the arrangement that allowed Germany and
Italy to build up their oil reserves in the years before World War II using expropriated
Mexican oil, until the British blockade put an end to the enterprise. "He is said", according to the
New York Times, to have won the arrangement thanks to an introduction to
Vicente Lombardo Toledano, a "powerful Mexican labor leader", provided by his longtime friend
John L. Lewis, head of the
CIO. Throughout his career, he faced numerous legal challenges, including a notable case in which a British court convicted him of defrauding a Danish oil company. In this case, the presiding judge called him "an unscrupulous and ruthless financier" and said "I do not accept him as a witness of truth." During the
1940 U.S. elections, Davis used funds provided by the German government to contribute approximately $160,000 () to a
Pennsylvania Democratic organization to attempt to defeat Sen.
Joseph Guffey, a Democrat and a prominent critic of Nazi Germany, and to attempt to bribe the Pennsylvania delegation to the
1940 Democratic National Convention to vote against Roosevelt, moves which both failed. The German government allocated $5 million (equivalent to $ million in ), stored at the German embassy, to support Davis's efforts. ==Controversy==