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.
"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.
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".
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.
Image caption: Some people protested the rally nearby
Democratic contender Bernie Sanders responded to the campaign launch by tweeting that Mr Trump 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.
Thousands of supporters gathered outside of the venue ahead of the president's rally.
Some had camped outside the Amway Center arena in Orlando since early Monday morning.
Mr Trump himself had claimed online the numbers numbered "thousands" two days in advance of his appearance.
CBS News reports many of the voters in the queue listed the economy and immigration among their top concerns – issues Mr Trump is sure to address throughout his campaign.
Protesters also attended and after a successful GoFundMe campaign, the Baby Trump balloon that took to the skies above London during the president's recent UK visit also put in an appearance.
Social media videos from the event appeared to show members of a far-right group, the Proud Boys, being stopped by police trying to confront anti-Trump demonstrators.
Image caption: Some Trump supporters have been waiting outside since 02:00 on Monday
President Donald Trump is facing a wide field of Democratic contenders in 2020. So who has a shot at becoming the next president?