Today, Joe Biden will quietly ring in his 80th birthday over brunch with his family in Washington. It’s a milestone none of his predecessors reached while serving in the White House and one that looms large as he considers his political future.

Yet the president enters his ninth decade at a moment of unexpected strength. Democrats defied history in the midterm elections, keeping control of the Senate and shattering Republican hopes of a “red wave” in the House.

The verdict – a beat-the-odds performance by his party and the defeat of several election-denying candidates backed by Donald Trump – offered validation to a president who saw the elections as a test of American democracy.

In the afterglow of the election, Democrats have piled on praise – a major reversal for Biden, who spent much of of the second year of his presidency weathering the blame for what many anticipated would be a crushing rebuke from voters. But instead of a repudiation, he found vindication.

“You did it, Joe!” Vice-President Kamala Harris exclaimed at a post-election event with supporters. “This victory belongs to Joe Biden,” Senator Elizabeth Warren of Massachusetts, his one-time rival for the Democratic nomination, said last week. And when asked how Democrats overcame tremendous headwinds and the weight of history, Jaime Harrison, chair of the Democratic National Committee, credited the president: “I have to thank Joe Biden.”

With the midterms behind him, and a possible reelection campaign before him, Biden’s allies are hopeful voters will come to see the first half of his term as they do: a hard-won success story.

Biden entered the White House at a period of profound tumult for the nation: in the shadow of the 6 January insurrection and the depths of the coronavirus pandemic. While vowing to confront the nation’s most urgent crises and shore up America’s standing abroad, Biden set out in pursuit of an ambitious agenda.

“He’s a president who understands the moment,” said Donna Brazile, a former chair of the Democratic National Committee. “And when we look back at this period, we’re going to see him as ‘steady Joe’, someone who was able to stabilize the country and move us forward.”

In less than two years, Biden has achieved a slew of consequential policy goals, some with the bipartisan support he promised. Taken together, the legislation he signed during the first half of his term has transformed the American social safety net and provided the largest investment to fight climate change in US history.

With narrow Democratic majorities on Capitol Hill, he helped push through a Covid relief package so large in scale that it halved the rate of child poverty in America. The new administration meanwhile expanded and accelerated a mass vaccination campaign that has inoculated nearly 7 in 10 American adults, though a post-pandemic return-to-normal has proved elusive.

Moving beyond Covid, he has amassed even more legislative wins: a $1tn investment in the nation’s infrastructure, the first gun control measure in decades, funding to boost the domestic manufacturing of semiconductor chips, an expansion of benefits for veterans and, finally, after months of uncertainty, the centerpiece of his economic agenda, a landmark climate and healthcare law. Soon he may also sign into law a bill protecting same-sex and interracial marriages.

With his nominations, Biden has rapidly reshaped the federal courts, including the supreme court, where Justice Ketanji Brown Jackson now sits as the first Black female justice in American history.

“It is as transformative a list as we’ve seen in at least a generation, if not more,” said Jeffrey Engel, director of the Center for Presidential History at Southern Methodist University. “The number and the scope and the importance of things that Biden has gotten through is remarkable, period, but with a slim majority, especially.”

But his successes are not confined to Capitol Hill, says Biden’s team, which recently compiled a list on Twitter using small type to emphasize the sweep of the president’s achievements.

With his executive authority, Biden met progressive demands by pardoning thousands of Americans convicted of marijuana possession and forgiving federal student-loan debt for millions of borrowers, which is tied up in legal challenges. He also signed two executive orders attempting to protect access to abortion after the Supreme Court overturned Roe v Wade in June.

He ended the war in Afghanistan, though the chaotic withdrawal of US troops rattled Americans and allies alike. When Russia invaded Ukraine, Biden rallied Nato and led the global response – a role he promised to restore after Trump’s isolationist retreat.

And many Democrats now say Biden and Harris deserve credit for foregrounding the threats to democracy and reproductive choice during the midterms. Despite warnings from party strategists that those were not front-of-mind issues, Democrats now believe they helped counter Republican attacks centered on inflation and crime and delivered crucial victories in battleground states.

“It was critical in framing this election,” said Cornell Belcher, a Democratic pollster. “If you take out ‘democracy’ and you take ‘choice’ out of that election word cloud, it would have been a goddamn bloodbath.”

In his last major pre-election speech, Biden warned that electing candidates who denied the results of the 2020 election and wouldn’t commit to accepting the results in 2022 ​​was a “path to chaos”. The most high-profile of such candidates lost, while abortion helped propel Democrats in states where the right was under threat.

“That we fought this midterm election to a standstill and actually picked up a Senate seat, it is historic,” Belcher said.

Not everyone agrees that the election was a resounding victory for the president. Some have argued that the elections were a rejection of Republican extremism, not a reflection of Biden’s political strength.

To win, Democrats had to outperform Biden, whose approval ratings hovered in the low 40s, dragged down by pessimism over the state of the economy. According to 538’s tracking aggregator of public opinion polls, Biden’s numbers are lower at this point in his term than any president since Harry Truman.

“Ironically, he probably would have gotten more credit if he had done fewer things,” said Celinda Lake, a Democratic pollster who has worked for Biden.

Before Democrats could sell an initiative to the public, Lake said, they were already embroiled in their next legislative fight. ​But she said the White House would have a fresh opportunity to make their pitch for his agenda as the implementation of many of his plans got underway in the months ahead.

At an event with business and labor leaders on Friday, Biden assured Americans that they would soon feel the impact of the legislation he signed earlier this year limiting the cost of health care and energy prices.

“We passed them this year, but now they’re really going to kick into effect,” he said. “It’s going to accelerate in the months ahead.”

Republicans have found ​much attack in Biden’s rich record, blaming his spending policies for ​exacerbating inflation. They have also threatened to use their new House majority to investigate the Afghanistan withdrawal, aspects of his Covid response and his administration’s handling of the US-Mexico border.

Neither are Democrats uniformly satisfied. Progressives are still dismayed by Biden’s preference for bipartisanship and argue that he has much left to do to fulfill the bold promises he made as a candidate. While Biden’s student-debt forgiveness plan and some of his immigration policies have divided his party.

Democrats’ run of legislating will almost certainly give way to a new era of gridlock in a divided Washington next year. But with a Democratic majority in the Senate he can continue to fill judicial vacancies – and he will face renewed pressure to exercise his executive authority to act on issues like climate and immigration.

Biden has said his decision to run for president in 2020 was rooted in his alarm of the Trump presidency, specifically his predecessor’s refusal to condemn the white supremacist violence in Charlottesville. He saw his mission as not only to defeat Trump but to defeat the forces of Trumpism.

After the midterms, Biden declared those anti-democratic forces in retreat.

Days later, Trump, 76, announced that he would run again for president. Already the oldest president in American history, Biden, who would be 82 years old at his inauguration in 2025, now must decide whether he is up for a rigorous campaign, potentially against an old foe, and, should he win, four more years in the White House.

Two-thirds of midterm voters, including many Democrats, said they did not want Biden to run for re-election, according to exit polls. In surveys, voters rank the president’s age as a top concern. Biden has said it is a “legitimate thing” for voters to consider while insisting that he has the mental and physical stamina for the job.

Top advisers are already laying the groundwork for a 2024 campaign. Biden has said it is his “intention” to run again but would discuss it with his family over the holidays before announcing a decision, probably early next year.

History provides several examples of presidents who “perceived a mission and chose to only serve one term”, Engel said.

But, he continued, “there is no historical precedent for a president having the question of age be as prevalent as it is and simultaneously feeling that the country’s survival may hinge upon his running again.”

In an “unstable world”, with Russia issuing nuclear threats, Trump attempting a comeback and American democracy still under assault, Lake said voters would likely turn again to the candidate offering steady, tested leadership.

In 2020, Americans “chose stability over instability and democracy over authoritarianism and violence,” she said, “and that contrast still exists today, probably even stronger.”