President Donald Trump mocked the Democratic presidential contender Mike Bloomberg after he endured a tough night Wednesday in his first Democratic presidential debate.

"Mini Mike Bloomberg's debate performance tonight was perhaps the worst in the history of debates, and there have been some really bad ones," Trump tweeted early Thursday morning.

Bloomberg had failed to defend himself against the barrage of attacks by his Democratic rivals, who focused on his record of sexist comments and controversial policies as mayor of New York City.

Bloomberg's campaign said the candidate "was just warming up tonight" and was still a winner.

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President Donald Trump gleefully mocked the Democratic presidential contender Mike Bloomberg as "stumbling, bumbling and grossly incompetent" after the former New York City mayor endured a tough night Wednesday in Las Vegas for his first Democratic presidential debate.

"Mini Mike Bloomberg's debate performance tonight was perhaps the worst in the history of debates, and there have been some really bad ones. He was stumbling, bumbling and grossly incompetent," Trump tweeted early Thursday.

"If this doesn't knock him out of the race, nothing will. Not so easy to do what I did!"

The Democratic presidential candidates Mike Bloomberg and Elizabeth Warren at the Democratic debate in Las Vegas on Wednesday night. Associated Press

Bloomberg was the focus of relentless attacks from his five Democratic rivals on Wednesday and failed to adequately defend himself.

His most notable challenger was Sen. Elizabeth Warren, who attacked him over his record of sexist comments and challenged him to release women from nondisclosure agreements with his company, Bloomberg LP, so they could openly discuss any claims of sexual harassment.

Here is one of their exchanges:

Bloomberg: "We have a very few nondisclosure agreements."

Warren: "How many is that?"

Bloomberg: "Let me finish. None of them accuse me of doing anything other than, maybe they didn't like a joke I told."

His response provoked a groan from the audience.

Bloomberg has shaken up the Democratic presidential race since entering in November, rising to second in some recent national polls after pouring hundreds of millions of dollars into a slick advertising campaign and a large network of field operatives.

But onstage Wednesday night Bloomberg presented a more faltering figure than the one familiar to followers of his Twitter account, which has hit back at Trump's gibes with stinging one-liners.

Bloomberg's campaign manager said the candidate was "just warming up."

"You know you are a winner when you are drawing attacks from all the candidates. Everyone came to destroy Mike tonight," Kevin Sheekey said in a statement.

"He was just warming up tonight. We fully expect Mike will continue to build on tonight's performance when he appears on the stage in South Carolina next Tuesday."