President Joe Biden and his aides have concluded something in recent weeks: The Mr. Nice Guy approach isn't working.

By introducing vast new vaccine mandates he once opposed, Biden is fighting back against what the White House sees as the sabotage of their agenda by a petulant, politically motivated minority.

After months wasted trying to persuade elected officials with bipartisan meetings and citizens reluctant to get vaccinated through gentle outreach, Biden felt he had little choice but to call for more aggressive steps, according to interviews with nine senior aides and close allies.

The president's exasperation has been clear.

"What makes it incredibly more frustrating is that we have the tools to combat COVID-19, and a distinct minority of Americans - supported by a distinct minority of elected officials - are keeping us from turning the corner," he said on Thursday, referring to an estimated 80 million unvaccinated.

"We cannot allow these actions to stand in the way of protecting the large majority of Americans who have done their part and want to get back to life as normal."

Biden's vaccine mandates for all federal employees and larger companies come as the number of infections in the United States rises, the use of face masks return, newly opened schools shut, hospital beds fill up, and some Republican-led states defy recommendations from health officials.

Some 100,000 Americans are predicted to die from COVID between now and Dec. 1, more than the same period last year, bringing the US death toll to 750,000. The prospect of the return to normalcy that Biden promised just two months ago, during a July 4 "Independence from COVID" celebration, has given way in many quarters to uncertainty and fear.

Biden's vaccine mandate marks a turning point, said Julian Zelizer, a Princeton University presidential historian.

"What you're seeing is him confronting the reality of ... vaccine resistance," he said. "It's a little bit like his early views of Republicans on Capitol Hill, that you can persuade them through the right words and right demeanor. I think the administration has woken up to the reality that this isn't true."

As growth in vaccine rates began to slow, the White House launched a summer campaign that included offers of cash, door-to-door outreach, and setting up clinics at workplaces, festivals, and places of worship. They recruited social media influencers - from soccer moms to fashion bloggers to Disney star Olivia Rodrigo - to help spread the word.

Those efforts largely crashed into a wall of defiance and misinformation. As the highly contagious Delta variant of the coronavirus spread, the job growth rate in August was the slowest since January, and economists are shaving their growth forecasts for the months ahead.

The economy and Biden's legacy are on the line. Ultimately history - and Americans - will judge Biden on his ability to manage the Covid crisis, say historians and analysts.

"Everything flows from his ability to manage the pandemic, from our economic health to our physical health and to his political standing," Zelizer said.

The last two months have been politically challenging for the president, aides and allies said.

As anxiety about the virus fueled concerns about the economic recovery, the chaotic Afghanistan withdrawal drew criticism from Republicans and Democrats and sparked finger-pointing inside the administration.

The president's net approval among independent voters sank from 17 percentage points in February to zero in August, according to Reuters/Ipsos polling.

The mandates are likely to shore up Biden's popularity among the 75% of US adults who have received at least one vaccine shot, Democratic political consultants said.

"People who are vaccinated are just kind of over it," said Steve Schale, a strategist who runs the pro-Biden political group Unite the Country Inc, referring to resistance to vaccines. Private polling by Biden allies viewed by Reuters shows broad public consensus that the pandemic remains a major problem requiring action, and growing resentment against people unwilling to get shots.

The issue may become like taxation on cigarettes, Schale said - an imposition on the minority of people who smoke but which is favored by most Americans.

His group found wide majority support for vaccine mandates along the lines proposed by Biden this week in five election battleground states that flipped from supporting Republican former President Donald Trump in 2016 to the Democrat Biden in 2020 - Arizona, Georgia, Michigan, Pennsylvania and Wisconsin.

With the Democrats' slim Congressional majorities on the line in next year's elections, Schale said the party could thrive if the votes become "a referendum on whether people should take personal responsibility to get out of the pandemic."

Biden's new mandates will only energize his opponents, said Amy Koch, a Republican strategist in Minnesota.

"In this hyper-partisan environment, for him to put down executive orders requiring vaccines without getting any kind of buy in will for sure galvanize his critics," she said. "The pendulum could swing back."-Reuters