Every president enters the Oval Office with a full plate of issues to tackle. But some have had more urgent crises to deal with than others. 
Abraham Lincoln inherited a country on the brink of civil war, and his very election drove the South to secede. Franklin D. Roosevelt had to confront the Great Depression, still the greatest economic crisis in the nation's history. Barack Obama's first order of business was confronting the second-biggest economic crisis in the nation's history.
President-elect Joe Biden will join that class of presidents coming into office amid a crisis on Jan. 20. As he himself often tells reporters, he is facing four concurrent crises: a once-in-a-generation pandemic, the resultant economic fallout, a nationwide reckoning over racial justice and policing, and the global threat climate change poses (though few outside his own party recognize the fourth as a top-priority "crisis").
Biden and his allies also point to President Donald Trump and the policies they will look to undo in the first days of the new administration.
Several granular problems lie within those crises. Here's a look at some of those issues Biden will have to confront in his first 100 days in office.

Working With Republicans

The forces that drove the mob attack on the U.S. Capitol on Jan. 6 will not go away on Inauguration Day. That became clear later the same evening when 147 Republican lawmakers voted to object to the Electoral College votes from Arizona and Pennsylvania, two states that helped seal Biden's victory in November.
This came just hours after the riot, which was brought on by rhetoric from the president and other Republicans about a stolen election and the possibility of overturning the results. 
Those members still attempted to overturn the results and spread their false claims even after members hid in offices and under chairs in the House chamber or were evacuated as a violent horde of Trump supporters entered the Capitol and attempted to stop the certification of Biden's victory. Five people died.
Biden can take some solace in the fact that several Republican senators who planned to object earlier that day stood down after the attack. But the fact that so many still did, including more than half of the House Republican Caucus, indicates an incentive structure that will reward Republican lawmakers for treating Biden as though he is an illegitimate president. 
That sentiment can be managed for at least two years while Democrats have control of both houses of Congress. But history tells us that the party that holds the White House struggles in midterm elections, and Democrats will still have to contend with that even if now there appears to be some backlash against Republicans.

Getting the Cabinet Confirmed

Biden needs an executive branch with clear leaders before he can begin to address the myriad issues he faces. That starts with the confirmation of his 15 Cabinet secretaries and a handful of Cabinet-level positions.
The president-elect is so far sticking to low-key and even boring picks for key Cabinet posts, relying on people with years of experience and deep expertise in their respective policy areas. Several also have long-standing relationships and a built-in level of trust with Biden, like Tony Blinken, Biden's choice to lead the State Department.
But not all of Biden's picks fit that mold. For instance, he tapped California Attorney General Xavier Becerra to run the Department of Health and Human Services despite Becerra's lack of experience in healthcare administration.
Republicans seized on Becerra's lack of experience, but Biden may not need to take their opinions into account to get his Cabinet picks approved. Jon Ossoff and Rev. Raphael Warnock won the Senate runoff elections in Georgia, bringing the Senate math to 50-50 and giving the Democrats a majority-by-technicality. Vice President-elect Kamala Harris will cast the tie-breaking vote on any evenly split votes, and since Senate Republican Leader Mitch McConnell ended the filibuster on executive nominations, 51 votes is all Biden needs.
We've already seen this calculus play out in his picks for the last few Cabinet posts. Biden nominated Judge Merrick Garland of the U.S. Court of Appeals in DC for attorney general the day after the Georgia runoffs, passing over former Sen. Doug Jones (D-Ala.) who was seen as easier to confirm. Also, Republicans could have blocked Biden from filling Garland's seat on the second-most-powerful court in the land had they retained Senate control.

Additional Pandemic Relief

Congress just passed a $900 billion stimulus package and Democrats were already talking about more aid money before Trump even signed the bill.
Biden referred to the December stimulus package as a "down payment" throughout the negotiations on Capitol Hill. House Speaker Nancy Pelosi used similar language when Trump signed the bill after Christmas.
Democrats have a leg up in getting more relief passed after winning both of Georgia's U.S. Senate runoffs. With Vice President-elect Harris breaking the tie, the Senate could pass more relief through budget reconciliation, a process that allows budget-related items (like $2,000 checks for instance) to pass with a simple majority and avoid the filibuster. That strategy would not work for policy areas without a budget angle, such as immigration reform, but it serves the immediate need for pandemic aid.
Several provisions will need immediate attention. Most notably, a moratorium on evictions for properties receiving federal dollars of any kind will expire on January 31 if not extended. The same is true of an ongoing forbearance on federal student loan payments; that will also expire at the end of the month. Biden will have to decide how to proceed using executive action, if at all. He has previously suggested he would erase $10,000 in student loan debt for every borrower, although the provision would face major pushback from across the country, political and otherwise. 

Vaccine Distribution

Biden will inherit a nation in the middle of a historic vaccine distribution effort, and one that by most accounts is not going that great.
Currently, upwards of 25 million doses have been distributed. But states have administered less than 10 million of those doses, according to Bloomberg's vaccine tracker. At this rate, millions of vaccine doses could expire by the end of January because they are only cleared for 30 days of storage in the refrigeration units that most distribution sites use. 
Biden criticized the vaccine rollout and said he would accelerate it. In a speech just before the end of the year, Biden outlined his plan for vaccine distribution and pandemic control for his first 100 days. The plan includes administering 100 million vaccine doses, opening most K-8 schools, and requesting that all Americans wear masks for 100 days.
The president-elect will also need to organize more vaccine candidates and their associated rollouts while convincing skeptical members of the public of their safety and effectiveness.

Rebuilding Relationships With Allies

Biden has long said that one of his first presidential trips abroad will be to the United States' allies in the North Atlantic Treaty Organization (NATO) to begin rebuilding those relationships. While those countries and their leaders have so far seemed eager to welcome the prospect of a Biden presidency, it will not be back to "business as usual."
Trump's "America First" vision for U.S. foreign policy resonated with millions of people and wormed its way even further into Republican orthodoxy. In the European leaders' eyes, what assurance can Biden give that in four years things will not go back to the new norms Trump set? What do relations with the U.S. look like if every four years its posture toward the rest of the world shifts?
Rebuilding those relationships will also be key to Biden's goals of addressing climate change, as Trump created mistrust when he exited the Paris Climate Agreement. Biden can rejoin the climate accord with ease, but again European leaders will ask what happens if in four years a candidate who does not believe in climate science wins the White House?
These are questions Biden and his foreign policy team will have to confront come Jan. 20 and beyond.

Undoing Trump's Immigration Legacy — Sort Of

Biden promised throughout the campaign to wipe away Trump's mark on the immigration system and institute a bevy of new policies.
Some of them he will likely enact on his first day in office, like a reinstatement of the Deferred Action for Childhood Arrivals (DACA) program, which can be done by executive order. Biden has also promised to undo Trump's severe restrictions on travel from largely Muslim nations, another executive action.
However, his advisers in recent weeks cautioned against the notion that everything with Trump's fingerprints will be undone on the first day. National Security Adviser nominee Jake Sullivan and Domestic Policy Council chair designee Susan Rice told the Spanish wire service EFE that many of Trump's policies could take months to undo.
"Migrants and asylum seekers absolutely should not believe those in the region peddling the idea that the border will suddenly be fully open to process everyone on Day 1. It will not," Rice said, according to a translation of the EFE interview.
Biden also comes into the office in the shadow of former President Barack Obama's immigration policies and faces a push from progressives to be more open and welcoming than Obama, who some have dubbed the "deporter-in-chief" for the high rate of deportations in his two terms.
Biden faces a litany of challenges in his first days in office. Everyone will be watching closely to see which goals he follows through on, and which fall by the wayside.