President Donald Trump on Wednesday hailed Democrat Joe Biden's "incredible comeback" in the primaries race and signaled how he will attack the new frontrunner, saying he was surrounded by far leftists.

"It was a great comeback for Joe Biden, an incredible comeback when you think about it," Trump told reporters at the White House the morning after the Democrats' Super Tuesday polls.

Biden is running as a moderate, in contrast to his leftist rival Bernie Sanders, but Trump insisted that some of the former vice president's "handlers are further left than Bernie. That's pretty scary."

Biden was the deputy president during the Obama administration. 

Biden made a surprise victory in Texas during the primaries, a state which is seen as a key player in deciding who will finally lead the Democrats heading into the elections. 

Meanwhile, billionaire Democrat hopeful Michael Bloomberg on Wednesday dropped out of the race, but has thrown his support behind Biden.