Because it seems more important now, here is a recap of my assessment of the President's ability to withdraw from some controversial international agreements (see previous post here).

(1) The Iran nuclear deal (the "Joint Comprehensive Plan of Action" or JCPOA). This agreement is nonbinding. The Obama administration has specifically described it in that way, and that is the only way it is even arguably constitutional. (See my discussion here). It is not actually an agreement; it is (as its title declares) a "joint plan of action." As a result, President Trump can decide to adopt a different plan of action regarding Iran. (Of course, other countries that adopted the prior plan of action are under no obligation to change their approach, and it may be doubtful how effective a unilateral change will be).

Some people have argued that the Iran deal has become binding on the United States as a matter of international law as a result of UN Security Council Resolution 2231, which endorses the deal. If that were true, it would amount to an extraordinary bit if constitutional bad faith by the U.S. President -- that is, to negotiate and accept a deal as expressly nonbinding in order to satisfy U.S. constitutional requirements, and then "launder" it through the Security Council (where the U.S. has a veto) to turn it into a binding agreement. If this is what occurred, no subsequent U.S. President (or Congress) should accept any purported obligation achieved in this way. However, President Obama can't be charged with bad faith here: the administration denied that the resolution would convert the deal into a binding agreement, and indeed it doesn't. The resolution uses only nonbinding language -- for example, item 1 "Endorses the JCPOA and urges its full implementation on the timetable established in the JCPOA."

In sum, President Trump may constitutionally withdraw from the Iran deal if he chooses.

(2) The Paris climate agreement. This agreement, unlike the JCPOA, is binding as a matter of international law. (Again, see my discussion here). However, it is not part of the supreme law of the land in the Constitution's Article VI, because it was not approved as a treaty by the Senate nor incorporated into a statute by Congress. Thus President Trump would have a good argument that U.S. law allows him to repudiate it, even though that would violate international law. (He can also give notice of U.S. withdrawal pursuant to the agreement's terms, but -- per the agreement -- not for three years).

Some people might argue that, even if the agreement is not part of the supreme law of the land, it is nonetheless a law that the President must faithfully execute under the Constitution's take-care clause. (I have argued that the take care clause extends to customary international law obligations; I'm less sure it extends to obligations in nontreaty agreements). If that's right, then President Trump would have to argue that the Paris agreement is unconstitutional (because it should have been approved as a treaty). This is a plausible argument that I've made in prior posts: if the agreement imposes material long-term obligations on the U.S., then the Constitution requires it to be approved as a treaty.

The Obama administration has argued that the agreement is constitutional (within the President's independent power) because all of its material obligations are nonbinding. If so, President Trump need not repudiate the agreement; he can simply decline to comply with the nonbinding parts of it. Nothing in U.S. constitutional law even arguably obligates him to comply with nonbinding commitments made by a prior President.

In sum, the Paris agreement should not be a material barrier to President Trump because it is not part of Article VI supreme law, and (in the alternative) because it either imposes no material obligations or is unconstitutional.

(3) The Trans-Pacific Partnership. This agreement has been signed but not ratified. Assuming no action is taken on it prior to the inauguration, President Trump is under no obligation to submit it to Congress and he can withdraw the U.S. signature if he chooses (all as part of the executive power over foreign affairs).

(4) NAFTA (and other trade deals). This one hurts, because I think NAFTA has been enormously beneficial to the U.S. and to world trade. But NAFTA provides that the U.S. (or any other party) may withdraw on six months' notice. In my assessment, the President's foreign affairs power includes the power to withdraw the U.S. from the obligations of international agreements in accordance with their terms. I think this power extends even to international obligations incorporated in a treaty, and so part of the supreme law of the land; NAFTA is not so incorporated, so the argument for the President is even stronger. (For some objections and responses, see my prior post).

Related thoughts from Julian Ku here: How President Obama Gave President-elect Trump the Power to Undo the Iran Deal and Paris Agreement.