Jim Johnson, the former chairman of Fannie Mae who was one of three advisors tapped by Democrat Barack Obama to vet vice presidential candidates, resigned today after questions were raised about favoritism he may have received from Countrywide Financial Corp.

Insisting he had done nothing wrong, Johnson issued a statement saying that he did not want the flap over his mortgage to distract attention from Obama's run for the presidency.

"I would not dream of being a party to distracting attention from that historic effort," Johnson said. "I believe Barack Obama's candidacy for president of the United States is the most exciting and important of my lifetime."

Johnson, 64, ran Walter F. Mondale's 1984 presidential campaign and helped John F. Kerry in his vice presidential search in 2004. Johnson was part of a three-person team – including Caroline Kennedy and former Deputy U.S. Atty. Gen. Eric Holder – appointed by Obama to cull the prospective candidates for vice president.

The Wall Street Journal reported 10 days ago that Angelo Mozilo, chief executive of Calabasas-based Countrywide, may have provided favorable terms on mortgages to Johnson and other friends. Ever since Johnson and the Obama campaign have been on the defense.