Donald Trump on Saturday said he "took a bullet for democracy" as he addressed his first campaign rally since surviving an assassination attempt.

The former U.S. President also rejected concerns that he is a threat to America's democratic system.

"I'm not an extremist at all," the newly-crowned Republican presidential nominee continued at the rally in swing state Michigan, dismissing his reported links to Project 2025, a shadow manifesto from figures close to him that has been characterized by opponents as an authoritarian, right-wing wish list.

And he mocked the rival Democratic Party, roiled by unprecedented pressure for President Joe Biden to abandon his re-election bid amid concerns over his age and fitness to serve, if reelected, until 2029.

"They have no idea who their candidate is ... This guy goes and he gets the votes, and now they want to take it away. That's democracy," Trump told the 12,000-strong crowd of passionate supporters.

In the fiery but typically rambling speech, the Republican riffed on his hardline immigration views, espoused falsehoods about migrant crime and repeated his baseless claim that Democrats "rigged" the 2020 election.

He expressed admiration for foreign autocrats including China's "brilliant" Xi Jinping, whom he praised for controlling "1.4 billion people with an iron fist."

And he evoked the seconds after a gunman tried to kill him at a rally in Pennsylvania, when, bloodied and surrounded by Secret Service agents, he raised a fist and yelled for his supporters to "fight!"

The crowd in Grand Rapids chanted the word back to him multiple times Saturday, though some appeared to tire of the lengthy address after 90 minutes and began heading to the exits.

The rally represented a moment remarkable by any measure, with Trump back on the campaign trail exactly a week since the assassination attempt.

He wore a new, smaller, flesh-colored bandage over his right ear, grazed in the attack by a 20-year-old gunman who also killed one bystander.

But Trump, after his near-death experience, ignored his self-declared pivot to unity and launched into the divisive rhetoric that has marked his political career.

He hurled insults and invective, calling Biden "stupid" and a "feeble old" man, and branding Harris "crazy" and "nuts."

The Biden-Harris campaign dismissed the speech as Trump "peddling the same lies (and) running the same campaign of revenge and retribution."

Security was tight inside Van Andel Arena, amid questions over Secret Service lapses at the Pennsylvania rally – though there were few visible signs of enhanced law enforcement in Grand Rapids.

Biden's 'big decision'

Meanwhile, Biden loyalists continued to defend the embattled president as the drumbeat of calls for him to abandon his campaign grow louder.

The 81-year-old and his team have remained publicly adamant that he is staying in the race, though some reports suggest discussions have begun in his inner circle about how exactly he might step aside.

There has been massive speculation over who could replace him. As vice president, Kamala Harris appears best positioned.

Sen. Elizabeth Warren, a leading progressive, gave Harris a boost Saturday without turning her back on the president.

"Joe Biden is our nominee," she told MSNBC. "He has a really big decision to make.

"But what gives me a lot of hope right now is that if President Biden decides to step back, we have Vice President Kamala Harris, who is ready to step up, to unite the party, to take on Donald Trump, and to win in November."

Some Democrats, however, fear such a late switch could trigger chaos, dooming the party at the polls.

Team Trump, for its part, is effervescent after an exceptional streak of luck – from surviving an assassination to favorable court rulings to Biden's disastrous debate performance last month.

Saturday was Trump's debut campaign appearance with running mate J.D. Vance, a 39-year-old U.S. senator with blue-collar roots who could help win over critical Rust Belt battlegrounds like Michigan and Pennsylvania.

Vance warmed up the crowd, taking a swipe at Harris.

"I did serve in the United States Marine Corps and build a business. What the hell have you done, other than collect a check?" he said of the former U.S. senator and California attorney general.

Trump supporters had begun lining up in their dozens in Grand Rapids a day before the rally began.

Edward Young, 64, was wearing a T-shirt showing the already iconic photo of Trump pumping his fist moments after being shot.

"They have turned him into a martyr and left him alive," he said.

"Now he's more powerful than ever."