He wants to break both entities apart. Well, Brexit worked.

To supplement my memory, here are some resources on the Trilateral Agreement. They are kind of randomly-selected opening paragraphs from a rich first page on a google search.


https://www.brookings.edu/research/the-trilateral-process-the-united-states-ukraine-russia-and-nuclear-weapons/
When the Soviet Union collapsed in 1991, Ukraine had the world’s third largest nuclear arsenal on its territory. When Ukrainian-Russian negotiations on removing these weapons from Ukraine appeared to break down in September 1993, the U.S. government engaged in a trilateral process with Ukraine and Russia. The result was the Trilateral Statement, signed in January 1994, under which Ukraine agreed to transfer the nuclear warheads to Russia for elimination. In return, Ukraine received security assurances from the United States, Russia and Britain; compensation for the economic value of the highly-enriched uranium in the warheads (which could be blended down and converted into fuel for nuclear reactors); and assistance from the United States in dismantling the missiles, missile silos, bombers and nuclear infrastructure on its territory. Steven Pifer recounts the history of this unique negotiation and describes the key lessons learned.

https://en.wikipedia.org/wiki/Nuclear_weapons_and_Ukraine
Prior to 1991, Ukraine was part of the Soviet Union and had Soviet nuclear weapons in its territory.

On December 1, 1991, Ukraine, the second most powerful republic in the Soviet Union (USSR), voted overwhelmingly for independence, which ended any realistic chance of the Soviet Union staying together even on a limited scale.[1] More than 90% of the electorate expressed their support for Ukraine's declaration of independence, and they elected the chairman of the parliament, Leonid Kravchuk as the first president of the country. At the meetings in Brest, Belarus on December 8, and in Alma Ata on December 21, the leaders of Belarus, Russia, and Ukraine formally dissolved the Soviet Union and formed the Commonwealth of Independent States (CIS).

After the dissolution of the Soviet Union, Ukraine held about one third of the Soviet nuclear arsenal, the third largest in the world at the time, as well as significant means of its design and production.[2] 130 UR-100N intercontinental ballistic missiles (ICBM) with six warheads each, 46 RT-23 Molodets ICBMs with ten warheads apiece, as well as 33 heavy bombers, totaling approximately 1,700 warheads remained on Ukrainian territory.[3] Formally, these weapons were controlled by the Commonwealth of Independent States.[4] In 1994 Ukraine agreed to destroy the weapons, and to join the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).[5][6]

https://theconversation.com/ukraine-got-a-signed-commitment-in-1994-to-ensure-its-security-but-can-the-us-and-allies-stop-putins-aggression-now-173481
Ukraine got a signed commitment in 1994 to ensure its security – but can the US and allies stop Putin’s aggression now?
January 21, 2022 9.27am EST