The 2004 Democratic presidential nominee on Monday praised Specter as a "fighter and a friend" and said he was "proud to vouch for his character." Kerry's press secretary, Whitney Smith, later said Kerry was endorsing Specter.
Specter is in a close race with Rep. Joe Sestak for the nomination. Specter raised questions about Sestak's Navy record and the lawmaker accused his rival of a "Swift Boat"-style attack.
In 2004, Swiftboat Veterans for Truth made unsubstantiated claims about Kerry's Navy record during the Vietnam War.
In his statement Monday, Kerry said he didn't want to referee a Swiftboat fight but did want to defend Specter's record.
