Congress can do little to halt the U.S. withdrawal from a nuclear arms control treaty with Russia, if President Donald Trump is determined to do so. But Democrats could have opportunities to shape and even block the administration’s plans to build up the U.S. nuclear arsenal.

Earlier this month, the White House announced it would leave the 1987 Intermediate-Range Nuclear Forces Treaty in six months. The Kremlin quickly responded that it too would cease honoring its arms control commitments under the accord, though the United States and NATO have long accused Russia of already violating the treaty by deploying an intermediate-range, ground-launched cruise missile.

The INF accord prohibits the United States and Russia from possessing ground-launched ballistic and cruise missiles with ranges from 500 to 5,500 kilometers (310 to 3,3417 miles). The thought behind the treaty was to limit the deployment of shorter-range nuclear weapons within or near Europe so that Russia and the United States would not be on a hair-trigger alert to use them within minutes if either thought the other was launching. The accord was a huge issue in Europe in the 1980s, with NATO allies in Europe pushing President Ronald Reagan to make the deal.

In recent years, Congress directed the Pentagon to research but not test military options for countering the advantages Russia might obtain by having intermediate-range missiles the United States does not also possess.

Most Democrats have criticized the INF withdrawal decision for, among other reasons, untying Russia’s hands to expand its deployment of ground-launched cruise missiles while the United States is years behind in developing such weapons. The U.S. also has no clear plan for where to base those weapons if and when they are acquired.

“By withdrawing from INF at this time, the United States is providing Russia with a pass on its obligations and giving them the unfettered and unconstrained opportunity to expand the deployment of their new missile system,” Senate Foreign Relations ranking member Robert Menendez of New Jersey said in a statement last week. “The U.S. does not have the assets in place to defend against Russia’s new missile, nor is it anywhere close to developing, manufacturing, and deploying a similar system that would operate as a counter to it.”

INF withdrawal and related issues — such as renewing the New START arms control accord with Russia and modernizing the U.S. nuclear arsenal — are likely to figure into the 2020 presidential contest.

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Most of the Senate’s Democratic presidential contenders have co-sponsored legislation from Oregon Sen. Jeff Merkley that would prohibit funding for the flight-testing, acquisition and deployment of U.S. ground-launched ballistic missiles with ranges banned by the INF treaty. That ban could be lifted when the administration fulfills a number of reporting requirements on the military rationale for such a weapon.

Notably, those conditions include identifying a U.S. ally that has formally agreed to host a U.S. intermediate-range ballistic missile. And if that placement is in a European country, the decision would need backing from all of NATO’S 29 member countries.

That could be a high-bar for the administration to meet, particularly in Europe given longstanding public opposition in Western NATO countries, such as Germany, to the redeployment of U.S. nuclear weapons on the continent.

Co-sponsors of the Merkley bill include Sens. Elizabeth Warren of Massachusetts, Kirsten Gillibrand of New York, Bernie Sanders of Vermont, Sherrod Brown of Ohio and Kamala Harris of California.

With so many high-profile presidential candidates coming out as early supporters of a legislative effort to stymie a potential push by the Trump administration to develop intermediate-range missiles, a normally insular and wonkish debate over nuclear weapons could get public attention in both the Democratic primaries and the general election, experts say.

“It certainly looks like this is going to be a big part of the congressional debate,” Elbridge Colby, a former deputy assistant secretary of Defense for strategy and force development in the Trump administration, said in an interview.

Colby, now the director of the Center for a New American Security’s defense program, said he was concerned that general anti-Trump sentiment among Capitol Hill Democrats would cause them to abandon their earlier support for funding the modernization of the U.S. nuclear arsenal under President Barack Obama.

“My lesser fear is there is going to be a lot of to and fro and probably less to show for it,” he said of the expected legislative skirmishes on nuclear weapons.

Legislative options

In addition to the Merkley bill, other anti-nuclear measures in the Senate have drawn the support of presidential contenders. They include a measure from Massachusetts Democrat Edward J. Markey that would prohibit research and development of the administration’s proposed low-yield, submarine-launched nuclear weapon. Warren, Sanders, Gillibrand and Merkley are all co-sponsors of the bill.

Markey has another bill that would make it illegal for the president to be the first to launch nuclear weapons in a conflict absent a declaration of war by Congress. That measure is co-sponsored by Brown, Gillibrand, Merkley, Sanders and Warren.

If one of those Democratic contenders wins the White House in 2020, nuclear weapons policies are expected to shift to the left of Obama’s.

Early in his administration, Obama agreed to Senate Republicans’ demand to rebuild much of the country’s Cold War-era nuclear arsenal in exchange for securing Senate approval of the New START accord, which imposes limits on the number of long-range nuclear weapons the United States and Russia can each deploy.

And House Democrats under Armed Services Chairman Adam Smith of Washington could use this year’s annual defense policy bill to place constraints on Pentagon and Energy Department funding for new types of nuclear weapons, including intermediate-range missiles.

Smith has routinely criticized as excessive and unaffordable the Obama and Trump administrations’ $1.2 trillion plan to modernize the country’s long-range nuclear arsenal.

“I’m encouraged by the fact that first of all, some of the new House leadership has put this on the public agenda, has said explicitly that these are topics that must be examined in public discussion and not only in closed committee hearings,” Thomas Countryman, Obama’s former acting undersecretary of State for arms control and international security, said in a conference call with reporters.

Anthony Wier, a former deputy assistant secretary of State for legislative affairs under Obama, said he was watching how the nuclear weapons debate is affected by the Democratic women pursuing the presidency.

“The other really fascinating wild card is as nuclear weapons policy comes back more into the political conversation, we’ve never had a major political conversation where women were really driving important parts of the discussion,” said Wier, now an anti-nuclear weapons lobbyist with the Quaker organization Friends Committee on National Legislation.

“I’m personally excited to see how that might change the conversation.”