President Obama will be formally sworn in to his second term in office today. The Constitution requires the inauguration to occur on Jan. 20, but since this is a Sunday, the ceremony will be private. A public inauguration, on the Capitol steps, will take place tomorrow, along with the celebrations that traditionally mark the quadrennial event.

So, the president will have the opportunity to savor his second-term inauguration twice. It’s a rarity, but perhaps a well-placed one, given all the challenges that face the president in the next four years.

Most urgent are the interrelated issues of the budget deficit and entitlements, particularly Social Security and Medicare. In his first campaign for president, Obama promised to attack the financial problems that threaten the health of those critical programs, but he broke that promise, focusing instead on health care reform. He can’t dodge the issue again.

Social Security and Medicare will be in trouble before long. The most recent report by Social Security trustees is that the retirement trust fund will be exhausted in 2033, and the Medicare trust fund in 2024, only 11 years away.

Given the need to begin reducing the nation’s massive budget deficits, and the obvious link between deficits and the high cost of entitlements – which are either overly generous or insufficiently funded – Obama must attend to them.

There is another reason for Obama to act. These programs are critical to tens of millions of Americans, but they are of little meaning to Republicans in Congress. Indeed, Republicans have been largely hostile to both programs since they were created.

It is unusual for either party to win three consecutive terms in the White House. Thus, there is a decent chance that a Republican, lacking affection for Medicare and Social Security, will be elected in 2016. It would be better for Americans of both political parties for friends of the program to drive the reforms that are inevitable. Obama must act.

Of course, more than just entitlements drive federal spending. Expenses went up with the recession that began in 2008; Democrats and Republicans, alike, must begin scaling those costs back. Obama should take the lead.

Military spending also needs to be in the mix, redirected in a way that makes sense given the changing nature of the threats facing the country. Indeed, that is the painful trade that Republicans and Democrats can make to begin the job of righting the federal budget.

The president has already begun one important task, thrust on him and the rest of the nation when a man wielding an assault weapon massacred 20 children and six adults in Sandy Hook Elementary School in Newtown, Conn. The package of responses he issued last week were appropriate to the recent string of mass murders. He needs to pursue that agenda, ensuring that members of Congress who are reluctant to approve the measures understand that they are in fundamental disagreement with a large majority of Americans.

What else? The economy remains weak. Climate change demands attention. Immigration reform has waited too long, continually derailed by Republicans who may finally have learned a lesson in the beating they took from Hispanic voters last November.

It all begins today, and Obama won’t have much time for bold action. Next year, Congress will become timid, awaiting mid-term elections. After that, attention will quickly turn to the 2016 presidential campaign.

The clock is ticking.