Mr. Trump takes over at a time of diverse and complex threats to American security. The new C.I.A. director will have to decide whether to undo a C.I.A. “modernization” plan put in place this year by Director John O. Brennan, and how to proceed if the president-elect orders a resumption of harsh interrogation tactics — which critics have described as torture — for terrorism suspects.
The nation’s top law enforcement official will have the authority for carrying out Mr. Trump’s “law and order” platform, including his threat to “jail” Hillary Clinton. The nominee can change how civil rights laws are enforced.
National Security Adviser
The national security adviser, although not a member of the cabinet, is a critical gatekeeper for policy proposals from the State Department, the Pentagon and other agencies, a function that takes on more importance given Mr. Trump’s lack of experience in elective office.
White House Chief of Staff
The chief of staff manages the work and personnel of the West Wing, steering the president’s agenda and tending to important relationships. The role will take on outsize importance in a White House run by Mr. Trump, who has no experience in policy making and little in the way of connections to critical players in Washington.
Stephen K. Bannon was also considered for chief of staff, but Mr. Trump instead named him chief strategist and senior counselor in the White House, saying that he and Mr. Priebus would be “working as equal partners” in the administration
Secretary of State
Whether Mr. Trump picks an ideologue or a seasoned foreign policy hand from past Republican administrations, his challenge will be that the State Department is the centerpiece of the post-1945 experiment of alliance-building and globalism, which Mr. Trump said he would dismantle.
The secretary will be responsible for government borrowing in financial markets, assisting in any rewrite of the tax code and overseeing the Internal Revenue Service. The Treasury Department also carries out or lifts financial sanctions against foreign enemies — which are key to President Obama’s Iran deal and rapprochement with Cuba.
The incoming secretary will shape the fight against the Islamic State while overseeing a military that is struggling to put in place two Obama-era initiatives: integrating women into combat roles and allowing transgender people to serve openly. Both could be rolled back.
The Interior Department manages the nation’s public lands and waters. The next secretary will decide the fate of Obama-era rules that stop public land development; curb the exploration of oil, coal and gas; and promote wind and solar power on public lands.
The agriculture secretary oversees America’s farming industry, inspects food quality and provides income-based food assistance. The department also helps develop international markets for American products, giving the next secretary partial responsibility to carry out Mr. Trump’s positions on trade.
The Commerce Department has been a perennial target for budget cuts, but the secretary oversees a diverse portfolio, including the Census, the Bureau of Economic Analysis and the National Oceanic and Atmospheric Administration.
The Labor Department enforces rules that protect the nation’s workers, distributes benefits to the unemployed and publishes economic data like the monthly jobs report. The new secretary will be in charge of keeping Mr. Trump’s promise to dismantle many Obama-era rules covering the vast work force of federal contractors.
Health and Human Services Secretary
The secretary will help Mr. Trump achieve one of his central campaign promises: to repeal and replace the Affordable Care Act. The department approves new drugs, regulates the food supply, operates biomedical research, and runs Medicare and Medicaid, which insure more than 100 million people.
Despite its name, the primary purview of the Energy Department is to protect and manage the nation’s arsenal of nuclear weapons.
Mr. Trump has said he wants to drastically shrink the Education Department and shift responsibilities for curriculum research, development and education aid to state and local governments.
Secretary of Veterans Affairs
The secretary will face the task of improving the image of a department Mr. Trump has widely criticized. Mr. Trump repeatedly argued that the Obama administration neglected the country’s veterans, and he said that improving their care was one of his top priorities
Homeland Security Secretary
The hodgepodge agency, formed after the attacks of Sept. 11, 2001, has one key role in the Trump administration: guarding the United States’ borders. If Mr. Trump makes good on his promises of widespread deportations and building walls, this secretary will have to carry them out.
The Environmental Protection Agency, which issues and oversees environmental regulations, is under threat from the president-elect, who has vowed to dismantle the agency “in almost every form.”
U.S. Trade Representative
The president’s chief trade negotiator will have the odd role of opposing new trade deals, trying to rewrite old ones and bolstering the enforcement of what Mr. Trump sees as unfair trade, especially with China.