A draft copy of the new Nuclear Posture Review that leaked out this month has set off a flurry of hand-wringing in Washington, especially since the draft says the administration is interested in enhancing its arsenal with smaller “low-yield” nuclear weapons.

The posture review will be released at the end of this week. In the meantime, policy experts are debating whether the changes mean the future of civilization is at greater risk, or whether the world is made safer if the U.S. nuclear umbrella has a broadened range of capabilities, not just multi-megaton weapons that could destroy life on the planet as we know it.

Where the experts and arms control advocates come down on this question depends largely how they view the bedrock premise underlying the rational use of nuclear weapons, namely that the sole purpose of having them is to ensure they are never used, a principle that goes by the simple word, “deterrence.” Deterrence, military strategists say, is not determined so much by what capabilities you have, but how your potential adversaries perceive that capability and how it affects their calculus.

Here are some of the arguments, pro and con.

1. Low-yield nukes are higher risk. The draft of the NPR envisions two new types of low-yield nuclear weapons. In the near-term it would add a smaller warhead to submarine-launched ballistic missiles, and then sometime in the future, develop a low-yield submarine-launched cruise missile. The U.S. already has a nuclear weapon with a variable yield option, the B-61 gravity bomb, which will be carried by stealthy F-35 fighters jets and the future long-range B-21 Raider heavy stealth bombers. The argument goes, large nuclear bombs aren't a deterrent if adversaries think the U.S. will never use them. Bombs that cause less destruction are more likely to be used, the theory goes, making them a more credible threat.

Pro: “Our goal is to convince adversaries they have nothing to gain and everything to lose from the use of nuclear weapons,” the draft NPR says. “In no way does this approach ‘lower the nuclear threshold.’ Rather, by convincing adversaries that even limited use of nuclear weapons will be more costly than they can countenance, it raises that threshold.”

Con: “I find that argument simply incredible. The U.S. today has this robust deterrent. It is capable of being employed anywhere in the world in defense of our interest and our allies within a matter of minutes,” said Joan Rohlfing, president of the Nuclear Threat Initiative, said at an Arms Control Association event this week. "Rather than raising the bar for nuclear use as they assert in the review, I believe it lowers the bar and makes their use more likely. This is destabilizing, not stabilizing.”

2. The triad is overkill. Like previous Nuclear Posture Reviews under former Presidents George W. Bush and Barack Obama, the Trump review affirms the necessity of maintaining all three legs of America’s nuclear triad: bombers, submarines, and land-based missiles. “The triad provides the president needed flexibility while guarding against technological surprise or sudden changes in the geopolitical environment,” the draft NPR states.

Pro: All of America’s commanders have endorsed keeping all three options available to the president. Submarines are the stealthiest option, intercontinental ballistic missiles the fastest, and bombers the most flexible because they can be recalled. “Eliminating any leg of the triad would greatly ease adversary attack planning and allow an adversary to concentrate resources and attention on defeating the remaining two legs,” the draft NPR says.

Con: Critics, most notably former Defense Secretary William Perry, argue that land-based ICBMs are too dangerous because the speed at which they can be launched risks miscalculation. "If you’re going to blow up the whole world, what is the hurry?” Perry told the PBS Newshour in 2016. “Why do you mind waiting another 20 minutes to do that? I don’t see either the common sense or even the strategic argument for doing that.”

3. The triad is unaffordable. The ambitious modernization plan to upgrade all three legs of the aging Cold War triad with new submarines, long-range bombers, intercontinental and cruise missiles, which was embarked on during the Obama administration is estimated to cost $1.2 trillion over the next 30 years.

Pro: “Maintaining an effective nuclear deterrent is much less expensive than fighting a war that we were unable to deter. Maintenance costs for today's nuclear deterrent are approximately 3 percent of the annual defense budget. Additional funding of another 3 to 4 percent, over more than a decade, will be required to replace these aging systems.”

Con: “It is clear to anyone observing the budget process that the current price tag of at least $1.2 trillion is completely unrealistic, and that adding to it would further draw resources away from capabilities and training that we need to most effectively counter our near-peer adversaries,” said Rep. Adam Smith, D-Wash., said in a statement “How President Trump plans to pay for these programs remains a mystery.”

“It's not a question of whether it's affordable, it's a question of whether it is sustainable, and it is a question of whether it's advisable,” Jon Wolfsthal, former National Security Council senior director under Obama, said at the ACA event. “It's a laundry list. We want every capability that's possible. … But none of these things are going to come in on budget or on time.”

4. This NPR is a major break with the past. Most of the draft document tracks with the kind of language you will find in the Bush NPR in 2002 or the Obama review in 2010. But critics say the changes, while subtle, are significant in both their substance and tone and have real world implications. In particular, they cite talk of an expanded role for nuclear weapons including responding to non-nuclear threats including that of a massive cyber attack.

Pro: The Lexington Institute’s Loren Thompson said Trump’s NPR approach is simply “an evolution that adjusts the posture in response to recent changes in the threat environment.” Writing in Forbes, Thompson argues that fielding low-yield warheads to discourage Russia from contemplating using similar weapons is not a major change. The draft report, he notes, labels the proposed additional weapons as “modest supplements” to the Obama plan.

“These supplements will enhance deterrence by denying potential adversaries any mistaken confidence that limited nuclear employment can provide a useful advantage over the United States and its allies,” the draft NPR states, citing Russia's limited nuclear first-use doctrine as a mistaken perception that must be corrected.

Con: “For years, the United States under successive presidents of both parties has consistently narrowed the circumstances under which an American president would contemplate use of nuclear weapons. For the first time in a long time, instead there is an expansion, an explicit expansion of the circumstances under which the president would consider such use,” countered Thomas Countryman of the Arms Control Association. The draft of the NPR “fails to give a convincing rationale why it has changed. It does not explain why the U.S. nuclear arsenal, still the most powerful and diverse possessed by any nuclear weapon state is insufficient to match threats on both the nuclear and the non-nuclear level.”

At the end of the day, the debate is always about how to prevent the use nuclear weapons by anyone in any circumstance, because any use would be a failure. And as for the concept of low-yield, tactical weapons, Air Force Gen. John Hyten, head of U.S. Strategic Command, told Congress last March that that’s a myth.

“I just fundamentally disagree that there is such thing as a tactical nuclear weapon,” Hyten told the House Armed Services Committee. “I believe that anybody that employs a nuclear weapon in the world has created a strategic effect; and all nuclear weapons are strategic.”