Trump had been wounded by a gunman at a campaign rally in Philadelphia.
But Fredericks, who spent a week preparing for the convention, remained confident that Trump would still come to Milwaukee, despite having come so close to death.
"He isn't going to hover in a corner," Fredericks said, who had flown in from New Jersey.
Fredericks marveled at how Trump, 78, raised his fist defiantly just moments after the assassination attempt on stage.
"No doubt about it. With him? The way he popped up after it happened. He's going to be here," he said.
And in Milwaukee, it is all systems go for the Republican convention that begins on Monday.
Trump's name is illuminated on large billboards along the city's main streets, the downtown area is under tight security, and hotels are packed.
Boost in support?
Michelle Altherr, a Republican convention delegate from Arizona who is voting for Trump, also said she remained confident in the former president.
"We're trying to wrap our heads around how this possibly could happen, but thank you God that there are angels that are protecting this man, because he will be the president in 2025, he will be elected this November."
Dave Simone, another Trump supporter, said he believed there is a possibility that the authorities were involved -- a popular conspiracy theory.
"There's a breach of security... That breach was intentional. Well, that's treason, and that person goes to Guantanamo Bay," he said.
On the other side of the political spectrum, Andzu came to Milwaukee to protest against the Republicans on Monday, but he too said he was shocked by the assassination attempt.
However, the 29-year-old said he is wary that the aftermath will become "political theater" and a distraction against campaign issues.
"Whether it was an actual assassination attempt against the Republicans or just political theater, whatever it doesn't change the fact that people are dying, that America is collapsing," said Andzu, who only gave one name.
Whatever their convictions, passers-by on the streets of Milwaukee agreed that the attack will play to Trump's advantage in the polls, despite his criminal conviction.
"We've just gone to another level as far as our support for Trump," Altherr said.
"Now there's going to be more people that are going to be supporting president Trump."
