WASHINGTON, March 23 -- Mike Bloomberg is transferring $18 million from his presidential campaign to the Democratic National Committee in the largest single such transfer ever.

It's the latest sign of the billionaire businessman's continued involvement in the race since ending his own campaign this month because of a lacklustre showing in the March 3 primaries. In those Super Tuesday contests, the former New York City mayor won only one US territory.

Bloomberg's contribution amounts to more than the national party's typical cash balance. The transfer will help the DNC make up for some of the steep fund-raising disadvantage when compared with its Republican counterpart, which routinely has raised tens of millions more than the Democratic o...