President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Thursday mocked Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE after the former vice president launched his campaign for the Democratic presidential nomination in 2020.

“Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign,” Trump tweeted.

The president warned Biden the race would “be nasty” and he would be forced to confront “people who truly have some very sick & demented ideas,” an apparent reference to other Democratic primary candidates.

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“But if you make it, I will see you at the Starting Gate!” Trump added.

Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign. It will be nasty - you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate! — Donald J. Trump (@realDonaldTrump) April 25, 2019

Biden made his long-expected presidential announcement in a video in which he criticized Trump for saying there were “very fine people on both sides” of the 2017 white supremacist rally in Charlottesville, Va., that turned deadly.

“With those words, the president of the United States assigned a moral equivalence between those spreading hate and those with the courage to stand against it,” Biden said. “And in that moment, I knew the threat to this nation was unlike any I’d ever seen in my lifetime.”

Republicans view the former vice president as Trump’s strongest challenger in a possible general election matchup.

Biden enters the Democratic primary as a leading candidate, according to polls, but he could face a tough race in a crowded field of candidates and in an environment where party activists are seeking a younger and more progressive nominee.

Trump nonetheless acknowledged Biden could be a serious contender in a tweet last week attacking him and Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.), another top-tier 2020 candidate.

“I believe it will be Crazy Bernie Sanders vs. Sleepy Joe Biden as the two finalists to run against maybe the best Economy in the history of our Country (and MANY other great things)! I look forward to facing whoever it may be. May God Rest Their Soul!” Trump wrote.

I believe it will be Crazy Bernie Sanders vs. Sleepy Joe Biden as the two finalists to run against maybe the best Economy in the history of our Country (and MANY other great things)! I look forward to facing whoever it may be. May God Rest Their Soul! — Donald J. Trump (@realDonaldTrump) April 16, 2019

Updated at 8:59 a.m.