President Biden warned on Wednesday that an “oligarchy” of the super-rich is emerging in America and warned of unchecked power as he delivered a farewell address to the nation just days before handing over office to a man he despises.

In an address from the Oval Office, Mr. Biden expressed concern about the “dangerous concentration of power” and argued for preserving democratic ideals and institutions under the administration of President-elect Donald J. Trump.

“Today, an oligarchy of extreme wealth, power and influence is taking shape in America, threatening literally our entire democracy, our fundamental rights and freedoms, and a fair opportunity for all to advance,” Mr. Biden said.

While Mr. Biden did not specifically call Mr. Trump by name, his remarks directly addressed the tensions at the heart of the new administration, where billionaires like Elon Musk are poised to wield enormous influence over the next four years. Are they really populists aiming to shake up the government to help working people left behind by the establishment? Or are they just billionaire disruptors looking to enrich themselves?

Mr. Biden’s warning about the emergence of an unelected oligarchy echoed a similar warning from President Dwight D. Eisenhower, who spoke about the military-industrial complex in his farewell address. The Biden version referred to the “techno-industrial complex,” warning of the erosion of truth itself brought about by uncontrolled social media platforms — a reference to Meta abolishing fact-checkers this week — and artificial intelligence becomes.

“Americans are being buried under an avalanche of misinformation and disinformation that enables abuse of power,” Mr. Biden said.

Mr. Biden, who has touted his record and achievements for months, did little of that on Wednesday. Instead, he spent more time urging Americans to remain engaged in the democratic process and to continue fighting for progress in areas such as combating climate change.

“The powerful forces want to use their unchecked influence to undo the steps we have taken to address the climate crisis to serve their own interests in power and profit,” he said. “We must not be forced to sacrifice the future, the future of our children and grandchildren. We need to keep moving forward and move faster.”

The speech in many ways capped not just four years in the White House but more than half a century of public service for Mr. Biden, who came of age in an era of politics that he no longer sees around him. It also served as a call for the country to remember its roots as he leaves the office he had longed for since his youth.

“After 50 years at the center of all this, I know that believing in the idea of ​​America means respecting the institutions that govern a free society,” he said.

“Our system of separation of powers, separation of powers — it may not be perfect,” he said, “but it has sustained our democracy for nearly 250 years, longer than any other nation in history that has ever attempted such a bold experiment.”

Mr. Biden called for term limits and ethics reform for the Supreme Court, as well as a ban on members of Congress from trading stocks.

And he called for changes that would protect against a recent Supreme Court decision that granted broad immunity to presidents, which Mr. Trump sought to use to mitigate several criminal charges and which could protect him while he faces retaliation and other autocratic acts in office Actions swears.

“We must amend the Constitution to make it clear that no president, no president, is immune from crimes he or she commits while in office,” Mr. Biden said.

In his final days and weeks in office, Mr. Biden has sought to cement his legacy as a transformative president who stabilized domestic politics while strengthening America’s leadership abroad. Hours before Wednesday night’s address, Mr. Biden celebrated the crowning achievement of his foreign policy record by announcing that Israel and Hamas had accepted a ceasefire agreement in Gaza that he proposed last spring.

But he is deeply unpopular. Even the location of the speech, behind the Resolute Desk in the Oval Office, is a reminder that Mr. Biden is not departing as he might have wished. In his last prime-time address there, in July, he explained why he dropped out of the presidential race under pressure from his own party amid questions about his age and suitability for another term.

Mr. Biden acknowledged that many of his policies had failed to resonate with Americans. “It will take time before we feel the full impact of everything we have done together,” he said. “But the seeds have been planted, they will grow and bloom for decades to come.”

Still, as recently as last week, he remained defiant about the presidential campaign, saying he believed he could have beaten Mr. Trump and that his decision to drop out was motivated by his desire to unite the Democratic Party.

Mr. Biden has told donors that he intends to remain involved in the party. When asked last week what role he would like to take on after the presidency, he replied: “I will not be out of sight or out of mind.”

Mr. Biden spoke for about 17 minutes, continuing the tradition of farewell speeches that dates back to George Washington. In 2021, Mr. Trump, who was politically isolated and facing impeachment after the Jan. 6 attack on the Capitol by a group of his supporters, said to those who had gathered to watch him take off from the tarmac at Joint Base Andrews in Watching Maryland: “Goodbye. We love you. We will be back in some form.”

As he said goodbye on Wednesday evening, Mr Biden called over his family, including his son Hunter Biden, who was in the Oval Office with his wife and their young son, and Finnegan Biden, one of the president’s granddaughters. “You are the loves of my life and the life of my love,” he said.

Vice President Kamala Harris and the second gentleman were also present as Mr. Biden concluded his speech. He called Ms. Harris an “incredible partner” and said she and her husband had become “like family.”

“Now it is your turn to stand guard,” Mr. Biden said in his final words to the country. “May you all be the keeper of the flame. May you keep the faith. I love America. You love it too. God bless you all. May God protect our troops. Thank you for this great honor.”

Peter Baker And Katie Rogers contributed to reporting.