On Twitter, supporters of the president praised his strength and hailed his message, calling him "Our beloved President" and "BEST PRESIDENT EVER!"
But for scores of families who've lost loved ones to the disease, as well as first responders and other advocates, the response was far different. Many of them slammed the president's cavalier sentiment and warned that it could make the situation worse.
Brian Walter, a New York City transit worker who lost his father to the virus, told ABC News in a statement that Trump's advice to people not to fear the coronavirus "hurts."
"It makes me worry for all the families who will still experience the loss of a loved one because our president refuses to take this pandemic seriously," he said.
Walter is a member of the survivor network and advocacy group COVID Survivors for Change, which has been documenting the toll the pandemic has left on millions of Americans. On Sunday, the group installed 20,000 empty chairs on the lawn across from the White House to symbolize the nation's COVID-19 deaths.
Chris Kocher, executive director of COVID Survivors for Change, said in a statement that he was taken aback by Trump's tweet, given that he had the best health care and treatment in the world -- a luxury that most coronavirus patients don't have.
Trump's doctors told the press that he was given several medications including an antibody cocktail, remdesivir and steroids.
"For the long haulers living with symptoms of COVID-19 for months on end, this virus is terrifying. Trump doesn’t care, and he still doesn’t get what families are going through," Kocher said in a statement.
Susan R. Bailey, the president of the American Medical Association, urged Americans to keep heeding warnings from doctors and health experts.
"We know vigilance is the best response to the COVID-19 pandemic because this virus doesn't feed on fear; it feeds on complacency," she said in a statement.
Liza Billings, a New York City nurse who lost her brother to the pandemic and is also member of COVID Survivors for Change, criticized Trump's take on the virus.
"I watched as medical teams fought like hell to save patients from COVID-19. All too often, this deadly and ferocious virus won," she said in a statement to ABC News.
Billings called Trump's message not to fear the virus a "slap in the face to all of those who lost a loved one to COVID-19, as well as all of us who put our lives on the line to save others."
"It’s a callous and dangerous remark that will do nothing to stop this horrifying pandemic, and may even make it worse," she said.
Among the more prominent voices speaking out was Kristin Urquiza, the Arizona woman who appeared at the Democratic National Convention and blamed Trump's rhetoric for her father's coronavirus-related death. Urquiza quote-tweeted the president's message saying, "At this point, the only thing we should be afraid of is you."
In a statement to ABC News sent later Monday evening, Urquiza said Trump is preoccupied with looking strong instead of focusing on helping the nation through the crisis.
"It’s more clear than ever before that Trump cares about no one but himself," she said.
While not referring to the president's tweet directly, former Vice President Joe Biden told a crowd in Miami that the president should listen to the scientists and medical experts about the dangers of the pandemic.
He noted that since the president was diagnosed with COVID-19 on Friday, more than 100,000 more Americans have contracted the virus.
"I hope the president’s recovery is swift and successful," Biden said, "but our nation's COVID crisis is far, far from over."
ABC News' Victoria Moll-Ramirez and Molly Nagle contributed to this report.
This report was featured in the Tuesday, Oct. 6, 2020, episode of “Start Here,” ABC News’ daily news podcast.
"Start Here" offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, Spotify, the ABC News app or wherever you get your podcasts.