WASHINGTON — President Biden has begun his second year in office by lashing out at Republicans, embracing forceful new attacks meant to define a choice for voters between Mr. Biden’s Democrats and a Republican Party still under the thumb of former President Donald J. Trump.

The sharp tone comes as Mr. Biden seeks to jump-start his agenda, which has largely stalled in Congress. And with midterm elections looming at the end of the year, the president faces a challenge that he has largely avoided so far: drawing Mr. Trump and other Republican leaders into a more direct clash of ideas.

On Thursday, Mr. Biden delivered a fierce speech promising a reckoning with Mr. Trump and pledging to use all of the powers of his office to thwart the anti-democratic forces unleashed by the 45th president. It was the most searing example since Mr. Biden took office of his effort to contrast the two parties, lamenting “the Big Lie being told by the former president and many Republicans who fear his wrath.”

A day later, he took another opportunity to focus on the differences between the two parties as he acclaimed news that the unemployment rate had dropped to 3.9 percent. He predicted that Republicans would accuse him of failing to address the economic pain caused by surging inflation in recent months.

“Malarkey,” Mr. Biden said. “They want to talk down the recovery because they voted against the legislation that made it happen. They voted against the tax cuts for middle-class families. They voted against the funds we needed to reopen our schools, to keep police officers and firefighters on the job, to lower health care premiums.”

“I refuse to let them stand in the way of this recovery,” he added. “Now my focus is on keeping this recovery strong and durable, notwithstanding Republican obstructionism.”

For some of Mr. Biden’s Democratic allies, the change in tone is a welcome shift from the dominant theme of the president’s first year, when he more often focused on his desire to unify the country and struggled to negotiate with members of his own party.

Now, they say, it is time for Mr. Biden to focus not only on his own achievements, but also on how the Republican Party threatens to reverse those efforts if it returns to power on Capitol Hill — something that has not been at the center of his presidency so far.

“What Biden, the White House and Democrats writ large have to do is to force a choice that takes into account not just Republicans criticizing, but what’s their solution?” said Robert Gibbs, who served as President Barack Obama’s press secretary during the year leading up to the 2010 midterm elections. “That’s going to be crucial heading into 2022 and then ultimately setting the table for 2024.”

Mr. Gibbs said Mr. Biden, then the vice president, would often advise Mr. Obama to keep the focus on their rivals in the other party.

“What he used to tell President Obama is: ‘It’s hard when you’re compared to the Almighty. It’s easier when you’re compared to the alternative,’” Mr. Gibbs recalled.

Republicans are not shrinking from the fight. Mr. Trump issued a statement describing Mr. Biden’s speech as “the last gasps of a corrupt and discredited left-wing political and media establishment,” and vowing to fight back at the ballot box.

The stakes are high. Mr. Biden and his party are at serious risk of losing their already bare majorities in the House and the Senate during the midterm elections, an outcome that would most likely rob the president and his team of any real hope of significant progress in Congress for the rest of his term.

And the obstacles to progress are steep.

During his first year in office, Mr. Biden has seen his policy efforts at home and abroad disrupted by Supreme Court rulings, supply chain glitches, lawmakers from his own party and, most of all, coronavirus variants that have extended — endlessly, it seems, to everyone’s dismay — the need for masks, vaccines and social distancing.

Mr. Biden has had some major successes to highlight: He passed Covid recovery legislation at the beginning of his term, and he found agreement with some Republicans on a $1 trillion measure to invest in infrastructure projects around the country.

But the virus is still rampant — a near-constant reminder of Mr. Biden’s campaign-year pledge to finally end the pandemic. His $1.8 trillion social policy legislation is struggling at best, and practically dead at worst. A voting rights bill he says will rectify an “existential threat” to the country faces the steepest of odds in Congress. President Vladimir V. Putin of Russia is beating his chest on Ukraine’s border. Every day, there is evidence that climate change is getting worse.

Democrats are hopeful that the president can begin to change those realities by March 1, when he will deliver his first State of the Union speech to a joint session of Congress, giving a formal assessment of the country under his leadership so far.

“It’s your best opportunity to get in front of the American people and make your argument about what you can get done before the fall and what the choice is going to be,” said Jennifer Palmieri, a veteran Democratic communications expert who worked for Mr. Obama and Hillary Clinton.

For that to happen, the Biden team needs to get a number of things right, according to people rooting for it to succeed.

The pandemic, which polls suggest is the single biggest drag on the president’s popularity, needs to begin to recede — at least in the daily lives of most Americans. And the administration needs to be seen doing more to address people’s frustrations, like the current shortage of Covid tests that have led to long lines and empty shelves at pharmacies.

Administration officials note that Mr. Biden authorized the purchase of 500 million at-home tests that Americans will be able to request for free. The first tests will ship this month, they say, with more to follow.

The economic rebound from the two-year pandemic may be one of the president’s best stories to tell on March 1. Job growth slowed somewhat in the second half of last year, but unemployment is so low that many employers are struggling to find workers. If he were giving the State of the Union address now, Mr. Biden could rightly claim to be presiding over a booming economy.

Still, inflation has driven up prices and that is adding to a disconnect for many people: They do not feel as good about the economy as the numbers suggest they should. Republicans on Friday seized on lower-than-expected job growth to attack Mr. Biden’s policies.

“Whether it’s anemic jobs growth, high inflation or a massive supply chain crisis, Democrats are doing a horrible job managing the economy,” said Mike Berg, a spokesman for the National Republican Congressional Committee.

Jen Psaki, the president’s press secretary, has repeatedly blamed people’s feelings about living in a pandemic for that disconnect.

“It’s less about data and more about what people are experiencing in their day-to-day life,” she said last week. “It doesn’t look normal. They’re worried about there being labor shortages and there being canceled flights, or not enough teachers in school because of the spread of Omicron. We understand that.”

Central to the administration’s response to those feelings is an effort to pass Mr. Biden’s social policy legislation, known as Build Back Better. The president argues that passage of the bill will lower prices for things like child care and prescription drugs, making people feel more secure about their financial futures.

But the legislation has become mired in a dispute with Senator Joe Manchin III, Democrat of West Virginia, who objects to some of the plan’s provisions and how it would be financed. In the Senate, where Democrats control exactly 50 of the 100 seats, Mr. Manchin’s support is essential to the bill’s passage.

The spectacle of the president locked in a desperate negotiation with a member of his own party has gone on for months, with little evidence of a resolution any time soon. White House officials say they are hopeful that lawmakers will be able to work something out with Mr. Manchin in the weeks ahead.

In the meantime, Mr. Biden is eager to avoid another foreign policy spectacle like the hurried evacuation from Afghanistan that followed the president’s withdrawal of troops. But that is not entirely within his control.

Mr. Biden has steadily ramped up threats of sanctions against Russia if Mr. Putin were to send troops across the border into Ukraine. Whether those threats will be enough to hold off Mr. Putin in the long run may help determine whether Mr. Biden has a positive story to tell by the time he addresses Americans in March.

White House officials are beginning to think about that speech. In comments to reporters on Friday, Mr. Biden was — as usual — upbeat, dismissing concerns that the burdens imposed by the pandemic would never be lifted.

“No. I don’t think Covid is here to stay,” he said, previewing the kind of message that aides hope he will be able to give in seven weeks. “The new normal is not going to be what it is now; it’s going to be better.”