Trump Has Promised Swift, Bold Actions as President. Will They Be Legal?

John B. Bellinger III is adjunct senior fellow for international and national security law at the Council on Foreign Relations.

Based on Trump’s 2024 campaign pledges and past actions, how could he wield executive power during his next term?

President-Elect Donald Trump is likely to take numerous actions domestically and internationally that will raise legal controversies just as he did in his first term. Some will be entirely new initiatives, while others will return to policies adopted during his first term but reversed by President Biden. Many will face legal challenges in U.S. courts and potentially even international tribunals.

What immigration actions could Trump take?

Trump has vowed to “carry out the largest deportation effort in American history.” Any plan to deport a large number of the more than eleven million undocumented immigrants in the United States would require a substantial increase in the number of immigration officials and judges to carry it out, and it would be costly. Trump has said he is considering using the U.S. military and relying on the 1798 Alien Enemies Act to facilitate deportations and internment of illegal immigrants. Both proposals would almost certainly face legal challenges in the courts. The 1878 Posse Comitatus Act restricts the use of the U.S. military for domestic law enforcement, and the Alien Enemies Act has only been used for deportation or internments during declared wars, most recently for the controversial internment of Japanese-Americans during World War II.

Trump has also said, “I will ban refugee resettlement from terror-infested areas like the Gaza Strip, and we will seal our border and bring back the travel ban.” It’s not clear precisely what Trump means by these pledges, but he is likely to reinstate some form of the controversial travel bans for individuals from Middle Eastern countries and to limit or prohibit refugee admissions from those countries. As in his first term, any new travel bans will likely face court challenges from human rights and civil liberties groups.

Is Trump likely to withdraw from the North Atlantic Treaty or other treaties?

It’s unlikely Trump would try to withdraw from the North Atlantic Treaty Organization (NATO) anytime soon, though he will certainly again push other NATO members to increase their defense spending and could try to pull out of the North Atlantic Treaty if they do not. Congress included a provision in the National Defense Authorization Act for 2024 prohibiting a president from withdrawing from the North Atlantic Treaty without the approval of Congress. The Trump administration could potentially take the stance that the provision is an unconstitutional restriction on the president’s powers. However, it would be awkward for Trump to ignore the restriction, given that it was co-sponsored with Senator Tim Kaine (D-VA) by Senator Marco Rubio (R-FL), Trump’s nominee for Secretary of State.

Trump could also withdraw the United States once again from the Paris Climate Agreement. He did so during his first term, but President Joe Biden rejoined on his first day in office. Trump could go further this time and try to withdraw from the UN Framework Agreement on Climate Change, a treaty that the United States joined in 1992 during the George H.W. Bush administration and under which the Paris Agreement (which is an executive agreement that does not rise to the level of a treaty requiring Senate approval) was negotiated. Because the UN Framework Agreement is a treaty approved by the Senate (by a two-thirds vote), some scholars argue that Trump could not withdraw from it without the same Senate approval. This question has never been resolved by the courts, but environmental advocates would certainly challenge its legality, likely requiring several years of litigation to resolve.

What about Trump’s approach to international organizations and tribunals?

A second Trump administration is likely to reverse the multilateralism of the Biden administration, including cutting off funding to, withdrawing from, and imposing sanctions on various international organizations. This is especially true of those that Trump believes are dominated by states hostile to the United States or Israel.

For example, the Trump administration is likely to refuse funding for the UN Relief and Works Agency for Palestine (UNRWA). Earlier this year, in response to evidence of involvement by UNRWA employees in the October 7, 2023, attacks in Israel, Congress suspended funding to UNRWA until March 2025. President Trump had previously cut off funding to UNRWA in 2018 and is unlikely to continue it, especially after Israel passed a law last month prohibiting UNRWA from operating inside Israel.

Trump could also withdraw again from the UN Educational, Scientific and Cultural Organization (UNESCO). The Biden administration rejoined the body in 2023—over the objections of Republicans in Congress—after the Trump administration pulled out in 2017.

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Trump’s Foreign Policy Moments

2017–2020

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Trump had also withdrawn from the UN Human Rights Council in 2018. The Biden administration rejoined the Council in 2021 for a three-year term but earlier this year decided not to seek reelection for a second United States term.

Trump could also potentially reimpose U.S. sanctions on the International Criminal Court (ICC) and its Prosecutor, Karim A.A. Khan, to punish him for seeking arrest warrants for Israeli Prime Minister Netanyahu and former Defense Minister Gallant for alleged war crimes in Gaza. Trump’s former National Security Advisor Robert O’Brien, who remains a close advisor to Trump and who could be appointed to a top position in the new administration, has said “the corrupt prosecutors and judges” should be targeted with sanctions, including visa denial and asset freezing; Republicans in Congress have drafted legislation to levy such sanctions. The first Trump administration had imposed sanctions on the then ICC prosecutor and judges in response to the investigation of U.S. officials for alleged abuse of detainees in Afghanistan. The Biden administration terminated the sanctions against ICC officials after Khan decided to suspend the investigation. Although the Biden administration has criticized Khan’s indictment of Israeli officials, it has provided support (reportedly despite objections from the Department of Defense) to Khan’s indictment of Vladimir Putin for war crimes in Ukraine. Given Trump’s unusual affinity for Putin and stated desire to swiftly resolve the Ukraine conflict, a Trump administration could decide to end U.S. support to the ICC prosecution of Putin.

What about some of the big legal cases pending against Trump in the United States and Trump’s relationship with the Department of Justice?

Early in his administration, if not the first day, he is expected to order the termination of Special Counsel Jack Smith’s prosecutions of Trump and former Trump administration officials relating to the former president’s retention of classified documents at Mar-a-Lago and alleged incitement of the January 6, 2021, attacks on the Capitol. Smith reportedly plans to resign before Trump takes office.

Trump could potentially order an acting Department of Justice official to take these actions, or wait for the Senate confirmation of his new attorney general. A Trump administration could also order the release of all the internal communications of, or interviews conducted by, Smith’s special counsel team with the hope of finding evidence of political bias, though there is a risk that releasing witness interviews and other internal information could actually be embarrassing to President-Elect Trump.

More generally, Trump appears intent on exercising greater presidential control over the Department of Justice. In addition to his nominating one of his most ardent supporters, controversial Florida Congressman Matt Gaetz, to be his attorney general, he has said he plans to appoint three of the attorneys who defended him in his criminal cases to senior positions in the Department of Justice, including deputy attorney general and solicitor general. Presidents have traditionally not interfered with criminal investigations by the Department of Justice, but it is not clear whether Trump and his White House will continue to observe this norm.

Trump has said that he “absolutely” will pardon some of the more than 1,400 people who have been charged in connection with the January 6 attack on the Capitol, whom he has called “patriots” and “hostages,” prompting a rebuke by at least one federal judge hearing the cases. It could be easier for Trump to pardon persons who have pled guilty or been convicted of less serious, non-violent offenses and who have not been sentenced to prison time. It could be more difficult politically for Trump to pardon rioters convicted of more serious offenses, such as assaults on police officers, especially if law enforcement organizations object.

This work represents the views and opinions solely of the author. The Council on Foreign Relations is an independent, nonpartisan membership organization, think tank, and publisher, and takes no institutional positions on matters of policy.