The rally in Florida, similar in style to the ones during his presidential campaign, came on the back of an aggressive press conference in which Trump embarked on a lengthy tongue-lashing of the media.
He also defended the achievements of his presidency so far, insisting that a spirit of optimism was sweeping the US.
A visibly frustrated and agitated Trump vowed to never let the media "get away with lies".
The President said he wanted speak to his supporters without the filter of "fake news".
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He alleged that the media has its own agenda. "And their agenda is not your agenda."
Though it wasn't clear what exactly Trump was "campaigning" for, he sought to assure his supporters that all was well with his administration, rebutting allegations that there were differences within the White House.
The event organised by Trump's 2020 re-election committee is just the latest example of the never-ending campaign culture in modern politics, experts say.
"The dishonest media, which has published one false story after another, with no sources, even though they pretend they have them. They make them up in many cases," he said.
"They (media) just don't want to report the truth. And they've been calling us wrong now for two years. They don't get it. But they're starting to get it," he said. "They have become a big part of the problem. They are part of the corrupt system."
He claimed that many American presidents "fought with the media and called them out often on their lies".
It has been a chaotic four weeks for Trump. The tenure began with a controversy over the size of his inauguration crowd, which was followed by US federal courts halting his executive order that imposed a travel ban on immigrants from seven Muslim-majority countries.
patriots who love their country, who salute their flag, and who pray for a better future. I also want to speak to you without the filter of the fake news," Trump said.
He also repeated some of his major campaign promises like keeping the US safe by strengthening its borders. He vowed to rebuild the country's military and develop a plan to "totally destroy" ISIS.
Trump also said he has started taking steps to bring back jobs to the country and "revive" the economy.
Earlier, talking to reporters travelling with him on Air Force One on his way to Melbourne, Trump said he was likely to make an announcement on the new National Security Advisor within a couple of days.
"I've been thinking about someone for the last three or four days, we'll see what happens. I'm meeting with that person. They're all good, they're all great people," he said.
Asked if it was too early to be holding a campaign event, Trump said, "For me, it's a campaign. To make America great again is absolutely a campaign. It's not easy, especially when we're also fighting the press," he said.