President-elect Donald Trump speaks during a meeting with House Speaker Paul D. Ryan (R-Wis.) at the Capitol on Nov. 10. (Zach Gibson/Getty Images)

Hillary Clinton

Donald Trump said he would put her in jail, accusing her of mishandling classified emails as secretary of state.

How would Trump be able to do that? To start, he would have to appoint his attorney general and then order the attorney general to select a special prosecutor to look into the matter. The special prosecutor would have to agree with Trump that Clinton violated federal law pertaining to the handling of classified information. Even then, Clinton would still be allowed a trial, at which the prosecutor would have to contend with the fact that the FBI investigation of Clinton found insufficient evidence to bring a case against her. FBI Director James B. Comey said in July that “no reasonable prosecutor” would bring a criminal case against Clinton.

Time frame: Trump could get the process started as soon as he comes into office if he appoints an attorney general willing enough to go after Clinton.

Obamacare

Trump has vowed to 'repeal and replace' Obamacare. He may find out that it's not quite that simple. (Video: Daron Taylor/The Washington Post)

Trump has pledged to repeal the Affordable Care Act and replace it with a set of new health-care programs.

Trump benefits from the fact that House and Senate Republican leaders share his goal. Congress probably can readily rescind parts of the ACA that involve federal spending, through a method called budget reconciliation — a strategy that produced a bill early this year that President Obama vetoed but Trump would sign. This method requires 50 Senate votes — one fewer than the GOP majority in the next Senate — and could be used to eliminate federal subsidies for ACA health plans, the requirement that most Americans have insurance, and other important elements. Because it would require 60 Senate votes to avoid a filibuster, Trump might have more trouble winning passage of some of his health-care proposals. They include converting Medicaid from an entitlement program to state block grants, allowing insurance companies to sell policies across state lines and letting individuals take tax deductions for their insurance costs, as businesses already do.

Time frame: Quickly for portions of the ACA to be abolished through reconciliation — as soon as the House and Senate scheduled votes. Unclear for the rest.

Waterboarding

Harsh interrogation tactics such as waterboarding, Trump said, should be used again.

Trump would have to appoint a team of lawyers to come up with a law that could win court approval. Trump would probably have to restart the program under a massive amount of public and congressional scrutiny. Former CIA director Michael Hayden has said repeatedly that the agency would not waterboard again, saying Trump would need “his own damn bucket.” Waterboarding had been a key part of the U.S. military’s Survival, Evasion, Resistance and Escape program and was used on trainees in controlled environments. In the early 2000s the CIA hired two clinical psychologists to create an interrogation program that incorporated aspects of SERE.

Time frame: Unknown. Trump would need to appoint a CIA director willing to direct his personnel to waterboard, as well as a defense secretary willing to do the same.

Donald Trump mused about accepting immigrants to the United States using a "merit system" during a campaign rally in Pensacola, Fla. (Video: The Washington Post)

The wall

Trump’s earliest campaign promise was perhaps his boldest — to build a “beautiful” wall along the Mexico border to keep out illegal immigrants and to force Mexico to pay for it.

To do this, Trump will have to work with two governments — Mexico’s and his own. His first step would be to persuade Congress to appropriate the money, which experts say could run into the tens of billions of dollars with Mexico refusing to pay. Trump has said he would force Mexico to pay by withholding about $24 billion in remittances to the country from illegal immigrants. But those are many of the same migrants he’s vowing to deport, and remittances also come from legal immigrants. To build the structure, Trump would also have to overcome major obstacles, including environmental and engineering problems; fights with people who don’t want to give up private land; and the huge geological challenges of the border.

Time frame: Trump says he'll start immediately, but given the myriad obstacles, this could take forever.

Deportation

In addition to the wall, Trump vowed to deport all illegal immigrants convicted of crimes, to remove many other undocumented migrants and to kill executive actions that protect some from deportation.

To do this, Trump has vowed to triple the number of U.S. Immigration and Customs Enforcement (ICE) agents, which experts say would require congressional approval and be very costly. He would also have to appoint an aggressive secretary for homeland security who would focus on measures to make it easier for ICE to deport the estimated 820,000 illegal immigrants who’ve committed crimes. Trump can end Obama’s Deferred Action for Childhood Arrivals program, or DACA, which has given temporary protection from deportation to hundreds of thousands of people who arrived in the United States as children.

Time frame: Targeting and deporting about half of the nation's estimated 11 million undocumented immigrants would take years.

Syrian refugees

Trump has promised “an extreme and total ban” on Muslim refugees entering the United States from Syria. More recently, he changed that vow, instead calling for an entry exam to determine “if hate is in their hearts.”

This would be an unprecedented step. The Trump administration’s first action would be a directive to the Department of Homeland Security to somehow design a test that certifies whether a refu­gee or asylum seeker from a majority-Muslim country is a threat. The agency would have to identify which citizens from which countries would be subject to such an exam, and he would have to persuade Congress to go along with it.

Time frame: This could take two years of drafting, analysis and hearings before final approval.

Iran nuclear deal

Another Trump pledge has been to renegotiate the deal aimed at curbing Iran’s nuclear weapons ambitions by imposing limits on some nuclear programs in return for lifting sanctions.

To pull it off, he would have to get all the parties that agreed on the deal, including the U.N. Security Council and Iran, back to the table to renegotiate some of the key tenets. If Iran deemed that to be a violation of the agreement, Tehran would be able to walk away from it altogether. Trump has said in the past that he has issues with some of the deal’s “sunset” provisions, specifically those that pertain to Iran’s enrichment of uranium. Under the deal it will be 15 years before Iran is allowed to make uranium that is weapons grade.

Time frame: However long it could take to get the U.N. Security Council and Iran, as well as Germany, back to a place where they would all want to renegotiate a hard-won deal.

Military

A signature Trump promise is to rebuild the military and cooperate with Russia in Syria.

To “rebuild” the military, Trump would have to persuadee congressional Republicans to roll back the defense budget sequester that affected force size and readiness levels. The sequester went into effect in 2013 but was a part of the Budget Control Act of 2011. According to the Committee for a Responsible Federal Budget, this would cost $450 billion through 2026. Trump would have to find a way to offset these costs and has proposed cutting the federal workforce to help do so. Trump has also pledged to cooperate more with Russia in Syria. This effort could be modeled by creating — much like the U.S. forces have done in Iraq — a joint intelligence cell in a neighboring country where the two countries could coordinate.

Time frame: Rebuilding the military could take years. But Trump could direct the Pentagon to start talking to Russia immediately if generals and intelligence briefings don't change his mind.

Federal workforce

Shrinking the size of the federal government through attrition and a hiring freeze is another Trump vow. Military, public safety and health employees would be exempt.

This doesn’t require congressional action. Presidents Jimmy Carter and Ronald Reagan imposed hiring freezes by issuing executive orders. Reagan issued such an order on his first day in office and made it retroactive to Election Day. These days, agencies have installed hiring freezes to avoid layoffs. Unlike in previous calls for a freeze, Trump’s goal isn’t to save money; it’s to clean up what he calls corruption and special interests in Washington.

Time frame: As Carter and Reagan showed, this can start in a snap. Meaningful results, however, will take years.

Oil and gas

Trump has promised to expand drilling for oil and gas and lift regulations on companies that dig for coal.

This responsibility would fall to the Interior Department. Trump’s interior secretary would have to instruct staffers to draft a new policy on energy excavation on federal land to replace the muscular regulations that restrict the practice. That would take a year of drafts and public hearings before approval. It would be complicated by a sour energy market. Even with regulations, the industry managed to excavate so much of the resources that they flooded the market. With too much supply, global prices fell, the industry suffered losses and jobs are still being cut.

How long: About 150 days, allowing for many court challenges from environmentalists.

Climate change

The Paris climate agreement reached late last year will be canceled, Trump has said.

Trump doesn’t have to do much to achieve this. He could simply shrug at the nation’s obligations under the accord. By failing to live up to the commitments promised by Obama under the agreement, Trump could throw the process into turmoil. If the United States doesn’t honor its vow to lower greenhouse-gas emissions, why should China, Brazil or India, which is racing to supply its vast and growing population with electric energy using coal? Experts say such a move would leave U.S. international credibility in shreds, but Trump has called global warming “a hoax” and has given little indication that his mind has changed.

Time frame: Ignoring an agreement takes no time at all. It might be a year or two before the international accord unravels.

Trade deals

Here’s what Trump said in June: “I am going to withdraw the United States from the Trans-Pacific Partnership.” He also vowed to “immediately renegotiate” the North American Free Trade Agreement, or NAFTA.

Trump can withdraw from the TPP literally by doing nothing. The agreement doesn’t take effect until it is ratified by all of its 12 signatories, and under federal law, Congress can’t ratify the deal until the president submits it. Renegotiating NAFTA is more complicated. Trump can propose changes to his counterparts in Mexico and Canada, but they are under no obligation to negotiate. Any NAFTA signatory can withdraw with six months’ written notice. But he could make trade a lot harder. Presidents have wide powers to impose tariffs or other trade restrictions without Congress’s approval.

Time frame: Immediately. Leaders in Congress say TPP is dead unless Trump revives it.

Amy Goldstein, Mike DeBonis, Jerry Markon, Lisa Rein and Eric Yoder contributed to this report.

Amy Goldstein, Mike DeBonis, Jerry Markon, Lisa Rein, and Eric Yoder also contributed to this report.