Obama starts running-mate search, Democratic source says

WASHINGTON (CNN) - Barack Obama is quietly beginning his search for a running mate.

A veteran Democratic activist in Washington told CNN that former Fannie Mae CEO Jim Johnson has accepted Obama's request for him to begin a screening/selection process for the No. 2 spot.

Johnson performed the same role in 2004 and 1984 for then-Democratic presidential nominees John Kerry and Walter Mondale.

The activist, a party operative who has been involved in democratic presidential campaigns and conventions dating back more than 20 years, said it is his information that the process is "at a very early point but that within the campaign itself they have been informally thinking about it for a while."

Obama campaign spokesman Bill Burton declined to comment on the report.