Donald Trump has launched a barely coherent attack on 2020 presidential rival Michael Bloomberg, suggesting the potential Democratic candidate has "tiny club head speed".

Mr Trump has been hitting the former New York City mayor hard since he jumped into the already crowded Democratic field.

"WOW, BLOOMBERG IS A TOTAL RACIST!" the president wrote in a tweet that has since been deleted. Those words were written over an audio recording in which a man who sounds like Mr Bloomberg explains he ordered the NYPD to put more officers in minority communities because those areas saw the most criminal activity.

A video of a radio interview Mr Bloomberg once conducted saying similar things also is circulating social media, the first major hurdle for the Democratic candidate since he entered the race.

A big reason why Mr Trump is targeting Mr Bloomberg as hard as any other leading Democratic candidate is polling data, which the president recently admitted he closely monitors.

A RealClearPolitics average of several hypothetical polls of a one-one-one general election race between the New Yorkers puts Mr Bloomberg ahead by 6 per centage points. Among the polls in that metric, two have the former mayor up by 9 points and another gives him an 8-point lead.

Mr Bloomberg is skipping the early Democratic caucuses and primaries, opting to formally enter the race on Super Tuesday. Mr Trump and others have accused him, due to his vast fortune, of buying his way into the race and onto the Democratic debate stage.

Of course, Mr Trump used his own wealth to finance much of his own 2016 campaign.