Following North Korea’s announcement of a moratorium on nuclear and intercontinental ballistic missile tests, a summit between Kim Jong Un, and President Donald Trump now looks likely to take place. If it does, it's also likely that the two leaders will agree on a joint statement that each will claim represents a historic victory. The positive short-term outlook for summitry should not, however, obscure the serious long-terms risks created by the latest spate of high-stakes diplomacy.

The United States’ diplomatic goal—the denuclearization of North Korea in the near future—is far beyond what is realistically achievable. The tensions that will be created by the almost inevitable collapse of diplomacy risk sparking a war. It is time to recalibrate expectations, therefore, and use the current diplomatic opening to launch an (admittedly un-Trumpian) risk-reduction process, focused on curtailing the threat from North Korea.

Trump appears to believe that North Korea has agreed to abandon its nuclear weapons. (It hasn’t.) And, even if Trump is more realistic in private, his—and his administration’s—public insistence that the complete, verifiable and irreversible disarmament of North Korea is the only acceptable outcome may leave him unable to accept anything less than the complete denuclearization of North Korea.

In fact, as the summit nears, U.S. goals appear to be getting even more ambitious. The White House’s latest definition of denuclearization seems to include the elimination of North Korea’s missile program. Moreover, Japanese Prime Minister Shinzo Abe may have convinced Trump last week that the United States should not make a deal with North Korea unless Pyongyang abandons its chemical and biological weapon programs.

Kim, by contrast, has not publicly committed to denuclearize, let alone give up chemical and biological weapons that he doesn’t admit to having. In fact, the North Korean statement announcing its test moratorium implied that it could afford to suspend nuclear and ICBM tests because the country had “realized the technology for mounting nuclear warheads on ballistic rockets.” It remains possible that Kim will agree to denuclearize at his summit with Trump—yet the odds of him following through on this commitment are effectively zero.

The North Korean regime almost certainly views nuclear weapons as a way of guaranteeing its survival. The United States would presumably offer it security guarantees in return for denuclearization—yet it is inconceivable that Kim would find them to be credible. After all, as North Korea likes to point out in its propaganda, seven years after Libya gave up its weapon of mass destruction programs, U.S. airstrikes led to the toppling of Muammar Gaddafi. To add to the challenges, the man responsible for convincing North Korea that its security won't be undermined if it disarms will be Mike Pompeo (assuming he is confirmed as secretary of state); yet, as CIA director he has openly advocated for regime change in North Korea.

These realities make a Trump-Kim summit very risky and potentially even a prelude to war. When diplomacy collapses, as it surely will, at the summit or in the months afterwards, tensions will likely rapidly escalate. Trump will probably feel able to justify the use of force on the grounds that diplomatic options have been exhausted. Indeed, he may well be encouraged in this stance by his national security advisor, John Bolton, who, shortly before assuming his current position, supported the idea of Trump-Kim summit as “a way to foreshorten the amount of time that we’re gonna waste in negotiations,” and separately, argued for the legality of pre-emptive strikes on North Korea.

Given the risks, the Trump administration should now rethink its headlong rush into a summit and a single-step denuclearization agreement. Without abandoning the long-term goal of ridding North Korea of its nuclear weapons, it should focus its diplomatic energies on more modest measures that would slow the pace at which the threat from North develops and ideally cap it. In return, Washington should offer Kim much less in the way of economic and security inducements than it would under the “Big Bang” approach—less for less, in other words.

The most obvious starting point would be North’s Korea moratorium on nuclear and ICBM tests, which is, in itself, a welcome development. Diplomats could be put to productive use trying to extend and formalize this moratorium by, for example, getting North Korea to agree to stop testing all ballistic missiles and space-launch vehicles (not just ICBMs) and convincing it to accede to the Comprehensive Nuclear-Test-Ban Treaty.

Trump need not walk away from the idea of a summit (indeed, he has invested too much political capital to do so). But he can and should instruct his Sherpas that he won’t sit down with Kim until the two sides have negotiated a concrete risk-reduction agreement that stands some chance of proving sustainable over the long term. This goal cannot be achieved by late May or early June, the target date for a summit, but it would help to ensure that, if a meeting between Trump and Kim does occur, it will represent a beginning—and not an end—for diplomacy.