Richardson Backs Obama, Rebuffs Clinton

"We have no plans of receiving an endorsement, but I would love to be pleasantly surprised. I've had many conversations with Gov. Richardson and I'm sure the Clinton campaign has. He is obviously a tremendously important leader in the country. He ran a terrific race this presidential season, and I think would make an enormous contribution to any candidate whom he chose to support," Obama said at the time.

Clinton Camp Downplays Impact

Friday the Clinton campaign appeared to downplay the significance of the coveted endorsement, with senior strategist Mark Penn pointing out Clinton's victory in New Mexico.

"Perhaps the time when he could have been most effective has long since past," Penn said, dismissing the practical value of Richardson's support after the New Mexico primary.

Richardson had stipulated two necessary criteria for a candidate to receive his endorsement.

In February, Richardson told The New York Times that the candidate should reflect the vote of his state and constituency. But he had also said the candidate with the most delegates after the March 4 primaries should be the Democratic nominee.

Though Clinton won the New Mexico primary, she won by only a very slim margin, and Obama still continues to have the lead in total delegates.

Richardson is the second former presidential candidate to endorse Obama.

Sen. Chris Dodd of Connecticut also endorsed the Illinois senator.

ABC News' Sarah Amos and The Associated Press contributed to this report.