WASHINGTON - When he ran for the White House, Joe Biden told voters his presidency would be a bridge to the next generation. His first two years on the job have revealed it to be a much more ambitious venture.

As he nears the halfway mark on his first term, President Biden is pointing to legacy-defining achievements on climate change, domestic manufacturing and progress on the COVID-19 pandemic — all accomplished with razor-thin majorities on Capitol Hill and rather dim views from the public.

President Biden’s legislative accomplishments extend to nearly every aspect of American life — although their impact may take years to be felt in some cases — and his marshaling of a global coalition to back Ukraine’s defenses and of democracies against China’s growing influence will echo for decades. He defied history in the midterm elections, persuading voters to stick with his vision of long-term gains despite immediate concerns about inflation and the economy.

It turns out his conception of the job is about far more than restoring democratic norms and passing the baton, as the 80-year-old president looks toward an announcement in early spring that he’ll run again despite his record-setting age.

The road ahead will be far tougher: Republicans take control of the House on Jan. 3, the threat of recession looms during stubbornly high inflation, and sustaining support for Ukraine will be harder as the conflict approaches the one-year mark.

The next two years also will be complicated by a heavy overlay of 2024 presidential politics. And whatever President Biden’s accomplishments, his job approval rating remains underwater and voters have expressed doubts about his capacity to lead. The president swats away questions about his ability to hold up with a dismissive “watch me.”

Commerce Secretary Gina Raimondo, echoing a refrain among presidential aides from chief of staff Ron Klain on down, says President Biden has been “frequently underestimated.”

“I don’t think he ever thought of himself as a caretaker,” she said. “He came in with an unbelievably ambitious agenda, and a core belief that he had to preside over many investments in America and American workers, American infrastructure, American manufacturing, that presidents had not done or not been able to get done for decades before him.”

In the 2020 campaign, President Biden offered himself as an experienced hand ready to step in to stabilize a pandemic- weary nation, but who also was mindful of a clamoring for fresh leadership.

“Look, I view myself as a bridge, not as anything else,” President Biden said in March 2020, as he campaigned in Michigan with younger Democrats, including now-Vice President Kamala Harris, Sen. Cory Booker of New Jersey and Michigan Gov. Gretchen Whitmer. “There’s an entire generation of leaders you saw stand behind me. They are the future of this country.”

A week later, he swatted back at primary rival Vermont Sen. Bernie Sanders’ agenda saying, “People are looking for results, not a revolution.”

Those statements have often been thrown back at President Biden by Democratic critics of two minds: moderates who have wanted him to curb the ambition of his agenda as he’s navigated an often rocky legislative path, and progressives urging him to step aside in 2024.

“Nobody elected him to be F.D.R.,” Rep. Abigail Spanberger, D-Va., told The New York Times pointedly last year as President Biden’s agenda appeared at a stalemate, a line that was seized on by House Republican leader Kevin McCarthy to critique the president’s agenda.

Meanwhile, some prominent Democrats have publicly declined to endorse Biden’s re-election when confronted with the question, and the progressive group RootsAction is running ads in New Hampshire — recently unseated by Democrats as the first state on the primary calendar — calling on President Biden to step aside for younger blood in 2024.

The president’s aides and allies argue that such critics miss the point — that the commander in chief never set out merely to keep the seat warm for the whippersnap- pers to follow, nor does he believe he’s finished the job. His successes of late have quieted many doubters — though some in his party still harbor private doubts.

“He couldn’t have thought about it more differently,” said Kate Bedingfield, the White House communications director and longtime aide to President Biden. “He’s leading with his experience, and the next generation is leading alongside him.”

Ms. Bedingfield pointed to President Biden’s relatively youthful Cabinet and to Democratic candidates across the country who won election in the 2022 midterms by running on the president’s agenda.

Says Democratic political consultant Jesse Ferguson: “He’s not giving a hand-off; he’s really giving a leg up to the next generation and people are responding to that.”

For restive young voters who may have once gravitated toward the younger crop of Democrats, Biden pollster John Anzalone said the president is offering proof of “getting things done for the new generation.”

“You saw that in how they voted in the 2022 cycle and you’ll see that in 2024,” he added.