A day after Barack Obama sealed the Democratic presidential nomination, obviously pleased members of the National Conference of Black Mayors assembled Wednesday in New Orleans for their annual meeting, calling Obama's win "a historic moment."  But the group won't be issuing an endorsement in the presidential race because of its nonprofit tax status. However, the organization's president Mayor George Grace of St. Gabriel, La. said during an opening news conference that "it would be very easy for you to guess" who the individual mayors will be backing. Although the group can't issue a unified endorsement, Grace said the conference would push to influence both the Democratic and Republican candidates on such issues as the economy, high gasoline prices, health care and the environment. Problems that affect the nation are "multiplied by 10" in the areas represented by the black mayors, Grace said. About 2,000 delegates are expected at the four-day meeting, which was moved on the fly to New Orleans after being originally scheduled for Detroit. The group switched cities in March after Detroit was hit by a scandal surrounding its mayor, Kwame Kilpatrick. He faces charges of perjury, conspiracy, obstruction of justice and misconduct related to explicit text messages sent to a former aide.