David Plouffe, a senior White House adviser who was President Obama’s 2008 campaign manager, accepted a $100,000 speaking fee in 2010 from an affiliate of a company doing business with Iran’s government. A subsidiary of MTN Group, a South Africa-based telecommunications company, paid Plouffe for two speeches he made in Nigeria in December 2010, about a month before he joined the White House staff. Since Plouffe’s speeches, MTN Group has come under intensified scrutiny from U.S. authorities because of its activities in Iran and Syria, which are under international sanctions intended to limit the countries’ access to sensitive technology. At...