The crowd chanted "Fight For Trump", "Stop The Steal" and "Four More Years".
Senior Republicans had urged Trump to encourage voting, rather than claims of electoral fraud. But he didn't stick totally to the script.
Trump said: "Our fight to drain the Washington swamp and reclaim America's destiny has just begun.
"We will not bend, we will not break, we will not yield, we will never give in, we will never give up, we will never back down. We will never, ever surrender."
Still, the President said winning in Georgia would be "revenge" for November 3.
He said: "The next great victory for our movement begins right here on January 5. And then we are going to win back the White House."
Trump added, "2024, a friend of mine said 'Oh, don't worry sir you're way up in the polls'. I said I don't want to wait until 2024."
A suggestion Trump supporters might boycott the Georgia elections began in the further reaches of the internet, on social media platforms like Parler. But over the past week it spilled spectacularly into the open.
Turn on the radio in Georgia and you will hear Lin Wood, a local celebrity lawyer and turbocharged Trump advocate, declaring: "This is Georgia, we ain't dumb. We ain't gonna go vote on January 5 on another machine made by China. You're not gonna fool Georgians again. Why would you go back and vote in another rigged election?"
Wood, 68, has represented Trump supporters in numerous high-profile cases across the country, including Kyle Rittenhouse, the teenager accused of killing two people at a protest in Kenosha, Wisconsin.
The lawyer's comments at a Georgia "Stop the Steal" rally, where former Trump lawyer Sidney Powell also spoke, lit a fire. It set alarm bells ringing, not just in Georgia, but in the White House.
The president personally telephoned Wood trying to calm the waters. Donald Trump jnr, hugely popular with the Trump base, recorded a radio advert telling supporters to vote, and calling the idea of a boycott "NONSENSE" on Twitter. Mike Pence, the Vice-President, was dispatched to Georgia on Air Force 2.
At a rally in Savannah at the weekend, Pence said: "Georgia, I came here to say 'Stay in the fight'. Stay in the fight to defend the Republican majority in the Senate. Stay in the fight until the polls close on January 5.
"I know we've all got our doubts about the last election. And I actually hear some people saying 'Just don't vote'. My fellow Americans, if you don't vote, they win!"
Pence added: "I want you to be confident about your vote. We're on 'em this time! We're watching! We're gonna secure the polls. Georgia, it all comes down to you. Georgia's got to hold the line."
If Pence's appeal sounded a little desperate, it was because these are desperate times for Republicans.
The party holds the Senate 52-48. If its two sitting Georgia senators lose, that will become 50-50. The new Democrat vice-president, Kamala Harris, will have the casting vote.
Keeping one seat means Republicans retain control, and with it the ability to block much of what Biden wants to do, including his selection of cabinet officials and judges.
In Pence's crowd there was some support for Wood and Powell, and their attacks on the Dominion voting machines used on November 3.
"I think they need to get it resolved before we vote again," said Barry Mann, 61, who was wearing a hard hat with a bald eagle on it. "I don't think the Dominion voting system will work (on January 5). I can see why people have a lot of questions..."
He added: "I'm not very happy with the governor [Republican Brian Kemp] right now. He needs to come clean, do a full investigation. They (Wood and Powell) are trying that right now. They're investigating the whole system."
One woman said: "My gut reaction was 'Hell, I'm not going to vote [on January 5]. Then I thought about it. I'm gonna vote."
Joseph Bazemore, 44, a Baptist pastor in a "Trump" T-shirt, said: "A lot of people were disgusted about voter fraud. But they can't give into that mindset. A boycott won't hurt them [the Democrats]. It hurts us. It doesn't make any sense."
The Senate races are destined to be close, and only a small number of Trump supporters staying home could be the difference.
In the latest polls Democrat candidate the Rev Raphael Warnock, 51, the black pastor of Rev Martin Luther King jnr's former church, leads Republican senator Kelly Loeffler, 50, by seven points. Jon Ossoff, 33, the other Democrat, is leading Republican senator David Perdue, 70, by two points.
Charles Bullock, a political science professor at the University of Georgia, said Republicans considering not voting because of perceived fraud was "really happening".
"It's resonated with people, crazy as it seems," he said. "So many Republicans live and die by what Trump says, and so if he says that the system's not to be trusted...the logical next step is, OK, so why bother to go vote?"
Trump lost Georgia, a state of 11 million people, by 12,000 votes. The resulting inquest has descended into an ugly Republican civil war, which is not helping the Senate re-election effort.
The President's most ardent supporters have taken to calling Kemp, the Republican governor, King George III, and chanting "lock him up" for not investigating claims of voter fraud.
Trump, Loeffler and Perdue are calling for the head of Georgia's Republican secretary of state Brad Raffensperger. He is now getting death threats.
"Someone's going to get shot," warned Gabriel Sterling, Georgia's top election official. "I have people outside my house."
The President's rally crowd was packed tightly together outside an airport hangar. Mask wearing was sporadic.
Trump claimed to have won Georgia and Wisconsin, both of which he lost, and said Democrats could only win if they cheated.
He said: "You know we won Georgia, just so you understand. They cheated and rigged our presidential election but we'll still win it. And they are going to try to rig this election (in Georgia) too.
"We've never lost an election. We're winning this election. I think I won the second one by more than I won the first one.
"When the numbers come out of ceilings and leatherbags what's going on? The swing states we're all fighting over, I won them all by a lot."
He added: "If I lost I'd be a very gracious loser. If I lost I would say I lost, and I'd go to Florida and take it easy and I'd go around and say I did a good job. But you can't accept when they steal and rig and rob."
Before the event, Trump telephoned Kemp, asking for an audit of signatures on absentee ballots, and a special session of the state legislature. Kemp refused.
The President lost Georgia by 12,000 votes. Trump told the rally: "This election was rigged and we can't let it happen again. Your governor could stop it very easily if he knew what he was doing Your governor should be ashamed of himself.
"Hundreds of thousands of illegal votes were cast in every state. We'll be going up to the Supreme Court very soon."
Trump said if the Senate races were lost America would be controlled by the "lunaric radical left".
He compared the Democratic Party to MS-13, saying both were "vicious but not stupid".
The President said, despite his own claims of fraud, his supporters must vote on January 5.
He said: "If you don't vote the socialists and communists win. We're going to watch every ballot. The answer is not to stay home. Let them steal Georgia and you'll never be able to look yourself in the mirror. Hold the line."
In the audience Connie Allen, wearing a Trump cowboy hat, said she still believed Trump could win the 2020 election but "it'll have to be through the courts". If he didn't, she strongly supported him standing in 2024.
She added: "I think there was absolutely fraud, probably more than we even know. I want to hear just that he's not giving up. I think there needs to be a complete overhaul of the voting system."
Richard Honeywell, 51, said: "There's always a chance he still wins this time, there seem to have been a lot of shenanigans. I'm not sure it can be said the election was secure in Georgia."
Asked if someone other than Trump should run in 2024, he said: "Donald Trump Jnr. I would say Dad but I'd take junior too, he's just as tenacious."
Ariana Morgan, 52, a photographer who travelled from New Orleans for the rally, said: "Absolutely to him in 2024. I hope by then the elections are actually fair and the issues resolved with fraud. He would definitely win. Just like he did this time.
"The Supreme Court needs to hear it otherwise 74 million people are going to be upset. We just want a fair election, we're not going to burn anything, if he loses we'll all go away and wait until 2024."
But Billy McIntosh, 71, a retired health and safety officer, said: "I think there's senators who could do just as well (in 2024). Trump just likes to say too much on Twitter. Someone should say, 'Man, you got to stop'. I liked Romney. Maybe him again"
Republicans face another problem - whether the two senators are "Trumpian" enough to excite the President's supporters.
Loeffler is the richest person in Congress. She and her husband are worth US$800 million and live in a jaw-droppingly beautiful US$10 million European-style mansion called "Descantes" outside Atlanta. She entered Congress as a moderate, but has since become an enthusiastic supporter of Trump.
However, at Pence's rally Republican voter Toni Hillhouse, 50, said: "She's not very relatable...I'm not a mllionairess."
David Hillhouse, 56, her husband, said both senators were "not conservative enough," adding: "These are the people we're stuck with unless we want the other side to win."
Another supporter of the President said: "I'd say they're probably both on probation."
Perdue, a wealthy former businessman, has faced controversy over his extensive share dealings while a senator. He has declined to take part in the final debate against Ossoff, a former investigative journalist who studied at the London School of Economics.
At a socially distanced rally outside a Baptist church in suburban Atlanta, Ossoff said: "David Perdue and Kelly Loeffler are like the Bonnie and Clyde of political corruption. It's cartoonish.
"David Perdue's campaign slogan now is that he wasn't criminally indicted. Maybe the bar should be a little higher for a sitting member of the Senate. Let's turn the page y'all."
Ossoff added: "Right now the eyes of the world are on Georgia. Victory comes down to young people. We have to let everybody know it's gonna be close, and we gotta get young people out to the polls."
Democrat voter Allison Waggener, 39, a classical singer holding a sign saying "You're Vote Is Sacred," said if some of Mr Trump's supporters decided not to go to the polls it would be very helpful.
"I sure hope so," she said. "I'm hoping that works."
