Bill Richardson, who sometimes seemed to be running to be Hillary Clinton's vice-presidential nominee, ended his presidential bid today after finishing fourth in both Iowa and New Hampshire.

"A year ago," Richardson said, "we were the only campaign calling for the removal of all our troops within a year's time from Iraq. We were the only campaign calling for a complete reform of education, including the scrapping of No Child Left Behind. And we were the campaign that was the most aggressive in clean energy and the most ambitious standards reducing global warming. Now, all the remaining candidates have come to our point of view. And I am confident that the next president of the United States will implement much of what we've been urging for the last 12 months, and our nation -- and our world -- will be better for it."

The tipping point for Richardson? He wasn't polling well in Nevada. As a Richardson advisor tells NBC, "It wouldn't do us any good to get our ass kicked" there.

No, especially if you hope to sell yourself as a V.P. candidate who can help swing the Western vote the Democrats' way.

In what may be another sign that he'd like to keep his vice-presidential options open, Richardson offered kind words for each of the other Democrats who've run but an endorsement for no one. He called John Edwards a "singular voice for the most downtrodden and forgotten among us." He said Barack Obama is a "bright light of hope and optimism at a time of great national unease, yet ... also grounded in thoughtful wisdom beyond his years." And he said Clinton's "poise in the face of adversity is matched only by her lifetime of achievement and deep understanding of the challenges we face."