President Barack Obama did in fact mention Democratic candidate for mayor, City Comptroller Bill Thompson, during last night's Democratic fundraiser: "Our great city comptroller, our candidate for mayor, my friend Billy Thompson is in the house." And that was it. Even Thompson himself, when asked if he thought it was an endorsement, said, "No. Do you consider that an endorsement?" (See for yourself—video is below.)
Still, Thompson's campaign was happy to take it, later issuing Thompson's "official" response soon after:
I am excited and proud to receive the endorsement of the President. To have the President of United States get involved in a New York City Mayoral race and endorse me, illustrates that he believes I will win and that I can lead this city.
A few weeks ago, White House press secretary Robert Gibbs made the President's endorsement of Thompson official with "The president is the leader of the Democratic Party and, as that, would support the Democratic nominee."