US President Donald Trump has formally launched his re-election campaign, urging supporters to "keep this team in place" for four more years.
The Republican president made his case before thousands of supporters at a rally in Florida, calling the state "my second home".
Mr Trump used the announcement to lash out at Democrats, accusing them of trying to "rip your country apart".
Early polls place Mr Trump behind some potential Democratic challengers.
He entered the stage with his wife Melania, who said she was "excited" to be first lady for six more years.
Senior figures from the White House, including Vice President Mike Pence and outgoing press secretary Sarah Sanders, also spoke at the rally.
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"Tonight I stand before you to officially launch my campaign for a second term as president of the United States," Mr Trump told supporters. "I promise you I will never ever let you down."
Florida is a key battleground state and one that Mr Trump narrowly won in 2016.
"We are going to keep America great again," the president told the Orlando event on Tuesday night, in a reworking of his familiar slogan.
Some supporters had been waiting since the early hours of Monday morning to see the president.
A counter-demonstration against his appearance was also held nearby.
What did Mr Trump say?
During his roughly 80-minute speech, Mr Trump reiterated key themes of his winning 2016 campaign.
He pledged to continue a crackdown against illegal immigration, one day after tweeting that US Immigration and Customs Enforcement (ICE) would soon begin removing "millions of illegal aliens" from the country.
"We believe our country should be a sanctuary for law-abiding citizens, not for criminal aliens," Mr Trump told Florida supporters.
He also accused Democrats of seeking to legalise illegal immigration in order to boost their voting base, and said they "want to destroy our country as we know it".
On no issue are Democrats more extreme – and more depraved – than when it comes to Border Security. The Democrat Agenda of open borders is morally reprehensible. It is the great betrayal of the American Middle Class and our Country as a whole! #Trump2020
Mr Trump described his opponents as a "radical left-wing mob" who he said would bring socialism to the US.
"A vote for any Democrat in 2020 is a vote for the rise of radical socialism and the destruction of the American dream," he told the crowd.
He also praised the economy, criticised the Mueller investigation into alleged collusion between the 2016 Trump campaign and Russia, and referred to media covering the event as "fake news back there".
The president also elicited "lock her up" chants from supporters when he brought up Hillary Clinton, despite her not being in the 2020 race.
A 'trial run' for his pitch to America
On Tuesday night in Orlando, Florida, Donald Trump "officially" kicked off his presidential re-election bid.
Of course, everyone knew he was going to run for re-election. That was hardly a surprise. He filed his 2020 paperwork the day after his January 2017 inauguration, and he's been holding regular campaign-style rallies across key battleground states ever since.
And so on Tuesday in Florida - one of the biggest of electoral battlegrounds, a state the president absolutely must win in 2020 - it wasn't about whether Mr Trump was going to seek re-election. It was about how he's going to do it.
The event was an unveiling of sorts - a trial run of his pitch to the American people for four more years, before a raucous, red-hat-wearing crowd packing a 20,000-seat arena.