Joe Biden just won the presidency. That may turn out to be the easy part.

The president-elect already was braced to deal with the worst health crisis the nation has seen in more than a century and the economic havoc it has wreaked.

Now, he has to build a government while contending with a Senate that could stay in GOP hands, a House sure to feature fewer Democratic allies and a public that includes more than 70 million people who would prefer that President Donald Trump keep the job.

There also is the looming question of whether Trump, who has claimed the election was being stolen from him, will cooperate. Traditionally, the transition process relies on the outgoing administration working closely with the incoming one, even if they are from different parties.

Biden’s top priority in the 10 weeks before Inauguration Day on Jan. 20 will be building a staff and assembling the pieces needed to tackle the coronavirus.

He’s likely to move quickly in announcing Cabinet picks and top aides central to dealing with the pandemic, including leaders of the departments of the Treasury and Health and Human Services and a National Economic Council director. That’s according to people involved in transition planning who spoke on condition of anonymity to discuss private conversations. Biden’s campaign declined to comment.

A senator for decades and vice president for eight years, Biden has a deep understanding of the workings of government, and he’s surrounded by a small group of top advisers with equally deep institutional knowledge.

“The Biden team is the most experienced, most prepared, most focused transition team ever, commensurate with the challenges that Biden will face" Jan. 20, said David Marchick, director of the Center for Presidential Transition at the nonpartisan Partnership for Public Service. The center advises presidential candidates on the transition.

A key member of Biden’s inner circle who is likely to move into a top administration job is Ron Klain, a former Biden chief of staff. Klain served as President Barack Obama’s Ebola response “czar” during the outbreak of that disease in the U.S. in 2014.

Advisers say Biden will assemble one of the most diverse Cabinets in history - but those choices won’t come without pressure. South Carolina Rep. Jim Clyburn, the third-ranking House leader whose coveted endorsement helped resurrect Biden’s flagging presidential bid early in the primary season, has already said he’d like to see the Cabinet include one of Biden’s best known African American advisers, Louisiana Rep. Cedric Richmond.

Transition work began months before Election Day and intensified in the three-plus days it took to declare a winner. The campaign even posted a transition website, although it didn’t link to any content while the race’s winner was still in doubt.

Biden will have to name 4,000-plus political appointees, including more than 1,200 requiring Senate confirmation.

Marchick said much of the work will be done by hundreds of Biden staffers quietly interacting with Trump administration counterparts. They will go to the agencies and ask “what’s happening, what’s in the pipeline, what regulations have just been issued, what regulations are about to be issued, what big problems they have,” Marchick said.

Traditionally, the Senate holds hearings for some key incoming Cabinet secretaries and other appointees before the inauguration to get them on the job quickly after the swearing-in.

The transition process formally starts once the General Service Administration determines the winner based on all available facts. That’s vague enough guidance that Trump could pressure the agency’s director to stall.

It’s also unclear whether the president would meet personally with Biden. Obama met with Trump less than a week after the election.

Regardless, Biden will have to grapple with how to fight a raging virus that has already killed more than 230,000 Americans and cost millions of jobs.

The pandemic also makes the business of assembling a government more difficult logistically. Though nearly all facets of Biden’s presidential campaign have been working remotely since March, his team will now have to adapt to a new, virtual workflow, including almost certainly interviewing top candidates via video conference.

Biden also must decide how to define the role of his running mate, California Sen. Kamala Harris. As vice president himself, Biden handled discrete portfolios for Obama, including the federal response to swine flu, economic recovery after the financial crash of 2008 and a gun-control push after the Sandy Hook school shooting.

There will be political headwinds. Control of the Senate may hinge on two Jan. 5 runoff elections in Georgia, which could mean campaign visits there by both Biden and Harris. Whatever the result, the Senate will be sharply divided, making it extraordinarily difficult to move major legislation.

If Republicans retain control of the Senate, it could be tough for Biden to get even key Cabinet nominees confirmed. Democratic Sen. Chris Murphy of Connecticut predicted Senate Majority Leader Mitch McConnell, R-Ky., “will force Joe Biden negotiate on every single pick.”

Biden promised to foster bipartisanship and to be a president for all Americans, including those who didn’t vote for him. That could open the door for some former Republican officeholders who endorsed Biden’s campaign to be tapped for key slots.

But it’s a balancing act for Biden. Too much bipartisan cooperation could draw the ire of leading progressives, who already are worried that Biden will scale back ambitious policy plans to combat climate change, overhaul the criminal justice system to fight systemic racism and expand access to health insurance.

Some on the Democratic Party’s left flank are pushing for two of Biden’s former presidential primary rivals to join his Cabinet: Massachusetts Sen. Elizabeth Warren as Treasury secretary and Sen. Bernie Sanders of Vermont at the Labor Department.

But Biden’s team might not want to provoke what would likely be fierce Senate nomination battles, much less vacate two Senate seats when Democrats need every vote.

Jeff Hauser, head of the Revolving Door Project, a progressive advocacy group that pressures Democratic administrations to appoint liberal nominees, said Biden could avoid Senate obstruction by aggressively using recess appointments.

The new president also could employ the Vacancies Act to place his top choices in acting executive branch roles for up to 300 days without Senate approval, then play a kind of musical chairs where he moves people between positions, Hauser said.

“It is a significant power,” Hauser said.

Some progressives are backing former Deputy Treasury Secretary Sarah Bloom Raskin for that agency’s top job, and Sherrilyn Ifill, president of the NAACP Legal Defense and Educational Fund, for Biden’s Justice Department. The left is generally far less enamored with the potential Biden choice for defense secretary of Michele Flournoy. She served as an undersecretary of defense under Obama but also has worked as a defense consultant.

Before Democrats get to arguing among themselves about Biden’s choices, there are bigger questions about the overall tone of the transition.

Republican President Herbert Hoover so detested his successor, Democrat Franklin D. Roosevelt, that the U.S. government was hampered even as a recession deepened, unemployment rose and Adolf Hitler came to power in Germany. That helped prompt the 20th Amendment, ratified in 1933, which moved Inauguration Day from March to January.

As a result, the country had less transition time between presidents to endure, but it also left a shorter time frame to do all the work required to build out a government.