Republican incumbent Rudy Giuliani could not run again due to term limits . As Democrats outnumber Republicans by 5 to 1 in the city , it was widely believed that a Democrat would succeed him in City Hall . However , billionaire Michael Bloomberg , a lifelong Democrat , changed his party affiliation a few months before the election in order to avoid a crowded primary , and ran as a Republican . The Democratic primary was meant to be held on September 11 but was postponed due to the September 11 attacks ; it was instead held on September 25 . The primary opened the way to a bitter run-off between the Bronx-born Puerto Rican Fernando Ferrer , and Mark J. Green , a non-Hispanic who attacked Ferrer 's close ties to Rev. Al Sharpton , leaving the party divided along racial lines
September 11 attacks
September 11 attacks
New York City mayoral elections