It seems US President Donald Trump is unshakable in his determination to nullify the legacies of his predecessor Barack Obama. After the Trans-Pacific Partnership agreement and the 2015 Paris climate accord, another Obama legacy with global significance－his push for a "nuclear-free world"－also looks shaky.

Though the Trump administration is scheduled to unveil its nuclear strategy in February, the draft of the new Nuclear Posture Review, which was leaked to the US media last month, has already generated waves, sending an unmistakable message to the outside world that the United States, instead of reducing the role of its nuclear deterrence, will seek to expand its nuclear capabilities.

In his first State of the Union address on Tuesday, Trump made no attempt to hide this strategic intention, declaring that the US needs unmatched military power and must modernize and rebuild its nuclear arsenal.

According to the draft nuclear review, the US will seek to expand "flexible US nuclear options", including "low-yield options", which are "important for the preservation and credible deterrence against regional aggression".

The logic behind the US decision to develop low-yield nuclear weapons may stem from the thinking that the current stockpile of US nuclear weapons is too big and too deadly to use, so it needs smaller ones to strengthen its nuclear deterrence.

However, this line of thinking is dangerous as it could lead to the opposite in reality: Instead of freeing the world from the threat of nuclear weapons, the US will add to the probability of a nuclear war in the future.

In contrast to the draft report's insistence that "it will raise the nuclear threshold and ensure that potential adversaries perceive no possible advantage in limited nuclear escalation, making nuclear employment less likely", some international observers have rightfully argued that the US pursuit of a new batch of smaller, low-yield nuclear warheads will lower the threshold on the use and deployment of nuclear forces.

The draft report's discussion on increased uncertainty and risk from a range of threats, including chemical, biological, nuclear, space and cyber threats, also suggests the US may use its smaller, low-yield nuclear warheads to address these new security challenges in the future.

If such a scenario emerges, it will change the unwritten rule on the use of nuclear weapons as the last resort and, thus, lead to disastrous consequences that even the US could not bear.

Since the end of World War II, the threat of mutual destruction by nuclear weapons, meaning the use of such weapons by one nuclear state against another would risk annihilating both, has prevented nuclear states from using such weapons.

But Trump's new nuclear policy seems set to change this unwritten rule and make a nuclear war more probable. If the reports are true, the new US nuclear policy should set alarm bells ringing across the world, because it not only marks a major departure from the one advocated by Obama but also signals a retrogression in the global push for nuclear disarmament and nonproliferation.

Apart from raising fears of a nuclear war, the new US nuclear policy will inevitably throw the global nuclear equilibrium off balance and trigger a new US-led nuclear arms race. Shortly after the US report was leaked, Russian Defense Minister Sergei Shoigu said his country's nuclear stockpile should be given a high-tech overhaul, suggesting the proportion of state-of-the-art weapons in Russia's nuclear arsenal be raised to at least 90 percent by 2021.

Indeed, the new US nuclear policy could become a signpost for recognized nuclear powers and the so-called nuclear threshold states to re-adjust their own nuclear strategies. In the face of the US expanding its nuclear capabilities, some states may seek to bolster their own capabilities and revamp their nuclear stockpiles.

If the US insists on lowering the nuclear threshold, it will lay bare its intention of bolstering its military supremacy, setting a bad example for other countries, especially for those with nuclear ambitions. And the international community will find it more difficult to stop countries such the Democratic People's Republic of Korea from pursing their dangerous nuclear programs.

The author is a senior writer with China Daily.