Billionaire Michael Bloomberg filed paperwork on Thursday with the Federal Election Commission to run for U.S. president as a Democrat, the latest sign that the former New York City Mayor is joining the crowded nominating contest. The filing allows Bloomberg to raise money in a bid for the White House, but an aide said on Thursday that no final decision on whether he will run has been made. Bloomberg, 77, has signaled that he plans a late-entry in the Democratic primary, suggesting he feels the field of nearly 20 candidates is vulnerable.