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…

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…

“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.”