Trump says he's terminating a major nuclear treaty with Russia. Here's what you need to know.

As National Security Adviser John Bolton was in Moscow, where he's expected to inform Russian officials of the Trump administration’s intention to withdraw from a major nuclear arms agreement -- the Intermediate-range Nuclear Forces treaty -- President Trump himself said Monday it definitely would happen.

"I’m terminating the agreement because they violated the agreement," Trump told reporters in Washington. "I’m terminating the agreement," he repeated for emphasis.

Asked whether he was threatening Russian President Vladimir Putin, Trump said, "It’s a threat to whoever you want. And it includes China, and it includes Russia, and it includes anybody else that wants to play that game. You can’t do that. You can’t play that game on me."

The INF treaty was a key to the end of the Cold War, reducing decades of nuclear tensions between the Soviet Union and the United States.

The dismantling of the INF Treaty could have major implications for U.S. foreign policy not just with Russia, but around the world. The treaty’s end would mark another step into a new world order, one less characterized by the détente and cooperation of the post-Cold War era.

What is the INF Treaty?

The Intermediate-range Nuclear Forces treaty banned the U.S. and the Soviet Union (and later, Russia) from deploying all ground-launched nuclear and conventional missiles with a range of 300 to 3100 miles. The treaty was signed in Reykjavik, Iceland, in 1987 by President Ronald Reagan and Soviet leader Mikhail Gorbachev, and led to the destruction of more than 2600 missiles by 1991.

Originally, the agreement covered only the U.S. and Russia. But Belarus, Kazakhstan, and Ukraine have joined the treaty as well. And though they are not formally part of the treaty, Germany, Hungary, Poland, Bulgaria, Slovakia and the Czech Republic have also destroyed their intermediate-range missiles.

The agreement is a major part of President Reagan’s legacy.

Why does the Trump administration want to withdraw from the treaty?

President Trump announced on Saturday that he will exit the agreement, citing Russian violations.

“We’re not going to let them violate a nuclear agreement and go out and do weapons and we’re not allowed to,” Trump said after a rally in Elko, Nevada.

In 2014, the Obama administration claimed the Russians developed and tested a prohibited cruise missile.

Earlier this year, NATO Secretary Jens Stoltenberg agreed that the Russian development of the 9M729 intermediate missile system constitutes a violation of the INF treaty. Russia has denied all allegations that they are in violation.

The Trump administration’s Nuclear Posture Review, which was released in February, had called the U.S. to research its own medium-range missiles carrying low-yield nuclear warheads to pressure Moscow, but it had also warned Russia's continued violations were making the treaty "untenable.”

Secretary of Defense James Mattis, speaking at NATO headquarters, made clear the administration’s patience on the issue was wearing thin.

“Russia must return to compliance with the INF Treaty or the U.S. will need to respond to its cavalier disregard for the treaty’s specific limits,” Mattis said.

Leaving the treaty is akin to finally calling the Russians out for the violation, according to ABC News Contributor and former Deputy Assistant Secretary of State Col. Steve Ganyard.

“The treaty was in name only, because only one side was abiding by it,” Ganyard said.

Are there any roadblocks to leaving the treaty?

The INF Treaty was ratified by the Senate, so there is some debate about whether the Trump administration requires congressional approval to abrogate the treaty.

Though the Constitution makes clear Congressional approval is required to create a treaty, "The Constitution is silent respecting withdrawal," Mary Ellen O’Connell, a professor of Law and International Dispute Resolution at the University of Notre Dame told ABC News.

"Presidents have consistently interpreted this silence to mean that he may withdraw under his foreign affairs power without the need for Senate approval,” O’Connell said.

Previous examples of the U.S. abrogating treaties include former President George W. Bush's decision to withdraw the U.S. from the 1972 Anti-Ballistic Missile Treaty (ABM), and former President Jimmy Carter's decision to withdraw from the Mutual Defense Treaty with Taiwan.

Because Congress did not register opposition in those cases, there may not be legal precedent for Congress to oppose the abrogation of the INF treaty.

What will happen if the treaty is dismantled?

Will there be a sudden proliferation of nuclear arms around the world if the INF treaty is no more? Not necessarily, experts say.

First, the process of withdrawing from the INF Treaty is somewhat complicated. The U.S. must deliver notifications and justifications of intent, and other parties to the agreement, like Ukraine and Belarus, have to be involved. Notification of withdrawal from one party to another kicks off a 6-month timeline before the withdrawal is complete.

It is possible that the U.S. and Russia could attempt to negotiate a broader arms deal during that 6-month period or create a multilateral deal that would involve China or other nuclear-armed countries.

But if the deal is dismantled after six months, U.S. intermediate-range missiles won’t necessarily start popping up across Asia and Europe. The treaty governed ground-based intermediate-range missiles, but the U.S. and Russia have always been free to develop missiles launched by air and sea.

“The U.S. doesn’t need to build ground-launched cruise missiles with this kind of range,” Alexandra Bell, senior policy director at the Center for Arms Control and Non-proliferation told ABC News. “We have intercontinental ballistic missiles and the most capable military in the world. This particular kind of missile, while it is provocative, we counter it in various ways.”

China’s influence

Still, the U.S. could be interested in using intermediate-range missiles to counter another emerging threat: China.

The INF Treaty was designed to remove missiles from Europe that had short reaction times and were difficult to counter, a major goal of the U.S. nuclear posture during the Cold War. Today, China’s growing military might is the strategic center point of U.S. nuclear strategy.

“From a U.S. perspective, we have a problem with China in that we have vast swaths of open ocean and long distances that would need to be defended if the Chinese were to move against allies like Japan or Australia,” said Ganyard. “There may be a reason for the U.S. to develop a longer range cruise missile to hold China at bay.”

Bolton echoed the idea that China is a major motivating factor in ending the deal during a radio interview in Russia today.

"But there is a larger question here - I think one that applies to both Russia and the United States - and that's the countries that are producing intermediate-range ballistic missiles and cruise missiles right now, specifically Iran, China and North Korea. We have this very unusual circumstance where the United States and Russia are in a bilateral treaty, whereas other countries in the world are not bound by it,” Bolton explained.

And China may be a major motivating factor for Russia, too.

“Russia’s got a very long border with China, longer than its border with Europe, so Russia may be looking to develop those nuclear weapons that could protect its eastern flank against a growing Chinese military capability,” Ganyard said.

ABC News's Patrick Reevell contributed to this report from Moscow.