Senator Joseph Biden of Delaware on Wednesday joined the crowded field of Democratic contenders in the 2008 White House race but his campaign quickly ran into controversy after his comments about a potential rival, Senator Barack Obama.

In an interview with the New York Observer published on the day he announced his candidacy, Biden made personal comments about Obama that critics said could be seen as racially insensitive.

Biden, 64, and a six-term senator, is the eighth Democrat to enter the presidential race, and often registers in the low single digits in polls behind senators Hillary Rodham Clinton and Obama and 2004 vice presidential nominee John Edwards.