By Liu Yang and Hu Ruoyu

US President Donald Trump said in his 2018 State of the Union address that the U.S. must rebuild its nuclear arsenal. He expressed that the U.S. hopes to never use nuclear weapons, but the nuclear arsenal should be strong enough to deter aggression.

The Huffington Post published a draft version of the Trump administration's new "Nuclear Posture Review" in early January. U.S. officials predict that the report will be released on February 2.

Compared to the version released eight years ago by the Obama administration, the Trump administration's nuclear weapons policy has made two significant adjustments. The first is to propose new nuclear warfare based on low-yield warheads and the second is to seek to ease the conditions for the use of nuclear weapons, according to media reports.

The document said that Russia keeps a large number of "non-strategic nuclear weapons" and has started to upgrade. The U.S. needs to make a symmetrical response so as to enhance diversity and flexibility of tactical nuclear weapons.

The document also hinted that the U.S. will expand its use of nuclear weapons and does not rule out the possibility using nuclear weapons first even in the absence of an imminent or actual attack.

These changeshave raised concerns both in the U.S. and abroad. 16 Senators including Dianne Feinstein and Bernie Sanders signed a joint letter on Jan 29 criticizing Trump administration's stance on nuclear arsenals.

According to the letter, the Trump administration ignores obligations under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) to achieve full nuclear disarmament, and increases the possibility of nuclear arms race and nuclear conflict.

Analysts believe that lowering the "nuclear threshold" cannot bring security; instead, it can only raise the risk of nuclear conflicts.

Wu Riqiang, an associate professor at the Institute of International Relations at Renmin University of China, said that once the low-yield tactical nuclear weapons have been used, they would have crossed the "nuclear threshold".

A Russian geopolitical expert said that the enemy will not know what sort of nuclear warhead it is and therefore a counterattack in this situation could lead to a nuclear war.

The same idea of using nuclear weapons to counter "non-nuclear strategic attacks" is also being questioned. The Trump administration has hinted that nuclear weapons may be used to fight against cyber attacks or terrorist attacks. Adam Mount, senior fellow at the Center for American Progress, said that such a change will undermine the credibility of the U.S. nuclear deterrence policy.

The superpowers started a crazy nuclear arms race to fight for global hegemony during the Cold War period. The huge nuclear arsenal became the sword of Damocles hanging over mankind.

After the Cold War, the logic of nuclear hegemony went bankrupt. The role of nuclear weapons should be limited to deter nuclear attacks. Hard-line nuclear policies cannot bring real security to the US, nor can they contribute to the strategic stability between nuclear powers.

The U.S. has one of the largest nuclear arsenals in the world and therefore it has a special and preemptive responsibility for nuclear disarmament. The U.S. should create favorable conditions for the eventual realization of complete nuclear disarmament, instead of indulging in the expansion of its nuclear arsenal and lowering the "nuclear threshold".