US President Donald Trump has officially kicked off his re-election campaign, with jabs at the media and political establishment at a rally of thousands of rollicking supporters.

Launching his campaign in Florida on Tuesday night (US time), Mr Trump exhorted the cheering crowd to keep advancing his political movement to put America’s “own citizens first”.

Florida is a key battleground state. Mr Trump narrowly won it in 2016 and must do so again to be re-elected in 2020.

Mr Trump walked on to stage at the packed Amway Centre in Orlando  with his wife Melania, who said she was “excited” to be first lady for six more years.

He reminisced about his 2016 campaign, describing it is as a “great political movement” and “a defining moment in American history”.

Mr Trump painted a disturbing picture of what life would look like if he loses in 2020, accusing his critics of “un-American conduct” and telling the crowd that Democrats “want to destroy you and they want to destroy our country as we know it”.

The apocalyptic language and finger-pointing in Mr Trump’s 80-minute speech made it clear that his 2020 campaign will probably look a whole lot like his improbably successful run three years ago.

“I have news for Democrats who want to return us to the bitter failures and betrayals of the past. We are not going back. We are going on to victory,” he said.

Mr Trump works the adoring crowd in Florida. Photo: Getty

Mr Trump spoke fondly of his 2016 run, calling it “a defining moment in American history”.

He said he had fundamentally upended Washington, staring down “a corrupt and broken political establishment” and restoring a government “of, for and by the people”.

But he also complained he had been “under assault from the very first day” of his presidency by a “fake news media” and “illegal witch hunt” that had tried to keep him and his supporters down.

Senior figures from the White House, including Vice President Mike Pence and outgoing press secretary Sarah Sanders, also spoke at the rally.

“He said he’d make America great again and that’s exactly what we’ve done,” Mr Pence said in his introduction.

“We’re here for one reason and reason only: America needs four more years of President Donald Trump,” he said, prompting a “Four more years!” chant from the crowd.

“It’s on,” Mr Pence added. “Time for round two.”

Don’t ever forget – this election is about YOU. It is about YOUR family, YOUR future, & the fate of YOUR COUNTRY. We begin our campaign with the best record, the best results, the best agenda, & the only positive VISION for our Country’s future! #Trump2020 pic.twitter.com/Vmu28hKQh6

— Donald J. Trump (@realDonaldTrump) June 19, 2019

Democratic contender Bernie Sanders responded to Mr Trump’s campaign launch by tweeting that the President was “living in a parallel universe”.

“Our most important job is to defeat the most dangerous president in the modern history of this country,” he said.

Leading Democratic contender Joe Biden took to Mr Trump’s preferred medium, Twitter, for his response to the campaign launch.

Hey there – @TeamJoe here. President Trump dismisses everything he doesn’t want to hear as “FAKE NEWS” — so as he announces his re-election, we want to make sure you have the real facts on his record:

— Joe Biden (@JoeBiden) June 19, 2019

Of course, Mr Trump has never really stopped running for president. He officially filed for re-election on January 20, 2017, the day of his inauguration, and held his first 2020 rally in February 2017, in nearby Melbourne, Florida.

He has continued holding his signature “Make America great again” rallies in the months since, while also raising millions to fund a more professional, far larger campaign operation, with about 80 staffers working at the campaign’s Virginia headquarters, in New York and in key states across the country.

Despite his perch in the White House, Mr Trump is hoping to replicate the dynamics that allowed him to capture the Republican Party and then the presidency in 2016 as an insurgent intent on disrupting the status quo.

-AAP