How desperate will Obama get, after voters repudiate Clinton, to save his legacy?

No U.S. president put more on the line than Barack Obama to ensure the election of his chosen successor. Now, Hillary Clinton's failure may serve as a repudiation of much of his two-term legacy.

From Obamacare to trade, from the Supreme Court to foreign policy and immigration, Donald Trump has vowed to systematically undo what Obama spent eight years putting in place. And the president made the stakes clear, telling supporters on the campaign trail that his accomplishments would go "down the drain" if the Republican won.

"America had never seen anything like Barack and Michelle Obama racing around the country frenetically on behalf of Hillary Clinton," said historian Douglas Brinkley. Obama "could not have put more energy or oomph into his endorsement speeches for her. But it just wasn't enough."

Now, Obama will struggle to preserve as much of his presidency as he can. He will meet with the president-elect at the White House on Thursday and said in a Rose Garden statement on Wednesday that he's ordered his staff to ensure a smooth transition. He said that the "remarkable work" of his administration had left Trump "a stronger, better country than the one that existed eight years ago."

'Sense of Unity'

Trump's gracious victory speech, Obama said, heartened him.

"That's what the country needs," he said. "A sense of unity. A respect for our institutions, our way of life, the rule of law. A respect for each other. I hope he maintains that spirit throughout this transition and I certainly hope that's how his presidency has a chance to begin."

Any attempt Obama makes to safeguard his legacy will focus on his hallmark legislative accomplishment, the Affordable Care Act, universally known as Obamacare. Trump has said he will repeal it, and he will enjoy the help of Republican majorities in both chambers of Congress.

Obama will pitch Americans to sign up for the program during the annual open enrollment period that's now under way. The president and his allies plan to stress that consumers' contracts with insurers are good through the first year of a Trump presidency. Additional enrollment in the program also would raise the stakes for congressional Republicans as they seek to repeal and replace the law without upsetting their constituents.

Signature Achievement

"The Affordable Care Act's on the line, and that's his signature domestic achievement," Brinkley said. 

Still, there is much in the health-care law that Trump can't overturn unless Democrats in the Senate agree, especially its guarantee of coverage for pre-existing health conditions. The political principle that all Americans should have health insurance may also be hard to undo.

The president is likely to fast-track consideration of those who came to the United States illegally as children and have sought shelter from deportation under an Obama program. While it's not clear how Trump will approach the initiative, the administration will doubtless work to enroll as many immigrants as possible for the three-year terms in hopes that revoking the status might prove politically unpalatable.

Carbon Emissions

Obama will also do what he can to lock in his environmental legacy. His aides pushed hard to recruit other countries to join the Paris Climate agreement, where nations agreed to limit global warming by reducing carbon emissions. The deal was formally put into effect during an 11-day international conference this week, binding the U.S. to the agreement through most of Trump's first term.

Trump has nonetheless said he will abandon the accord. He is likely to roll back the president's executive actions limiting American carbon emissions, but other nations -- including large polluters like China and India -- may still abide by their commitments.

Foreign Policy

Obama will also seek to solidify other foreign policy accomplishments targeted by Trump on the campaign trail. He'll try to reassure allies who are party to the international agreement limiting Iran's nuclear program, as well as the coalition battling Islamic State in Iraq and Syria, when he travels to Germany, Greece, and Peru this month.

Trump's election raises the stakes for Obama's last foreign trip, where he can expect to encounter leaders nervous about the future of their relationship with the U.S.

Still, some of the president's priorities seem unlikely to survive. The Republican made opposition to the Trans-Pacific Partnership -- the centerpiece of Obama's attempted strategic pivot to Asia -- a major plank of his campaign. The trade deal is effectively dead.

"The Constitution gives the president great authority in foreign and defense policy. He will set the tone and he will set the policy," said Nicholas Burns, a former undersecretary of State who's now a professor at Harvard University's Kennedy School of Government.

As president, Trump will have the power to ban immigrants from Muslim countries, bar refugees from Syria or other countries and abrogate international agreements such as the Iran nuclear deal, Burns said. He can also alter the commitments at the core of the NATO alliance and other international coalitions.

Still, Burns added, "There are all sorts of regulators on presidential behaviors. Congress is one, the American people is another, so is the press and the attitude of foreign leaders."

Should Trump withdraw from the Iran nuclear deal, Burns said, "there is zero chance" that Germany, Britain or France will agree to reimpose sanctions against Iran.

Supreme Court

The president also lost his chance to reshape the Supreme Court as a more liberal institution. Senate Democrats now face the dilemma of either approving a conservative nominee to the court, or filibustering in a way that disrupts the legislative norms of the upper chamber. That could lead Republicans to eliminate the power to filibuster -- the best remaining political weapon available to the minority party in the Senate.

There are other accomplishments Trump can't nullify. Pulling the U.S. out of the Great Recession following the 2008 financial crisis. Naming two Supreme Court justices, both women. Killing Osama bin Laden. The establishment of new national monuments.

"Nobody's going to take away from that," Brinkley said.

Nor will Trump and Republicans be able to easily reverse a Supreme Court ruling allowing gay marriage in all 50 states. 

Personally Popular

Despite Democrats' staggering loss on Tuesday, Obama himself remains popular with an approval rating of 56 percent, according to Gallup. Demographic patterns are changing in ways that will bolster the Obama coalition of young and minority voters over time. While Clinton's electoral loss was profound, more Americans likely cast a ballot for her than Trump.

Obama will retain an outsized bully pulpit as he leaves the White House. He plans to remain in Washington for at least two years, and aides say his post-presidency plans include political efforts to shore up Democrats in the state-by-state redrawing of legislative districts.

For a president who spent two terms redefining American politics, the work to shape his legacy just became a longer and harder process that's likely to extend far beyond his time in the Oval Office.