GRAND RAPIDS, United States (AFP) — Donald Trump is set to hold a triumphant first campaign rally Saturday since surviving an assassination attempt, in startling contrast to United States (US) President Joe Biden, who remains hunkered at home with COVID, resisting unprecedented Democratic pressure to step aside.

Ahead of Trump’s speech to thousands of passionate supporters in the swing state of Michigan, running mate JD Vance warmed up the crowd, taking a swipe at Vice President Kamala 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 US senator and California attorney general.

Meanwhile, Biden loyalists continued to defend the embattled president as the drumbeat of calls for him to abandon his campaign grows louder amid concerns over his age and fitness to serve, if re-elected, until 2029.

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, Harris appears best-positioned to do so.

Senator Elizabeth Warren, a leading progressive who sought the party’s presidential nod in 2020, gave Harris a boost Saturday without turning her back on the president.

“Joe Biden is our nominee,” she said on 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 that 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 the failed assassination bid to favourable court rulings and Biden’s disastrous debate.

The rally will represent a moment remarkable by any measure, with Trump striding back on stage exactly one week since a 20-year-old gunman on a Pennsylvania rooftop attempted to kill him.

“I had God on my side,” he told the Republican National Convention Thursday, at which he demonstrated his absolute control over the party, firing supporters up to a rare pitch.

Dozens of the most ardent Trump supporters began lining up Friday outside Van Andel Arena in Grand Rapids, Michigan for the Saturday rally at 5:00 pm (2100 GMT).

With less than an hour to go before he was scheduled to appear, the 12,000-capacity arena was nearly full.

Edward Young, 64, preparing for his 81st Trump rally, was wearing a T-shirt showing the already iconic photo of Trump pumping his fist immediately after being shot.

“They have turned him into a martyr and left him alive,” he said, adding, “Now he’s more powerful than ever.”

Just as Trump’s convention address shifted quickly from a plea for unity to harsh attacks on the Biden administration, he seems certain to assail Biden and Harris on Saturday over illegal immigration, inflation, crime, the wars in Ukraine and Gaza, China policy and oil drilling.

All eyes, however, will be on the security posture, especially given questions over Secret Service lapses at the Pennsylvania rally.

The Van Andel Arena is enclosed, allowing more complete control of the perimeter. Security nevertheless is expected to be extra tight.

It will be Trump’s debut campaign appearance with Vance, a US senator from Ohio who at age 39 could help win over critical swing states like Michigan, Pennsylvania and Wisconsin.