Nuclear, biological or chemical?
My answer has always been the one we are under attack from now - biological. Covid-19 is a test run - targeting who China most would like to eliminate - elderly because they are costly non-producers - and blacks - with the population explosion in Africa threatening China's growing economic interests there. It also is a tactic warning from China. Since we get everything from China - even most food now is from or processed in China, they could kill virtually every American by an unstoppable biological attack before we knew anything was happening - and then about it. Regardless, most of us are dead, dying or inevitably will be infected - all while China (or other attack) says "we didn't do it, it just came out of nature!"
We also see the benefits to biological attacks too.
Deniability: You can kill hundreds of thousands or millions, devastate the adversaries economy and society, while denying any responsibility or alternatively claim it was an accident.
Harm to adversary: Covid-19 has permanently destroyed hundreds of thousands of small businesses, soon to top over half a million, with small business the largest employer in the USA. The unemployed reached 40 million. The national debt will have increased 50% in not much more than a year - and the costs and harms - economic and to society will last for years and may keep getting worse as more and more lethal stains of it are released or evolved.
Killing the enemy: The Wuhan biological warfare gain-of-function covid-19 is claimed to have killed 350,000 Americans and the number rapidly growing. If this continues, it will be the most deadly war the USA has ever been in - with nothing but profits and benefits to the attacker. Brilliant strategy by China.
Profitability: China is at the same time making trillions off this as people no longer spend money at restaurants, travel, road trips and going to amusement parks or the theater. Rather, they spend that money buying from Amazon and WalMart - 95%+ being Chinese products. Even most masks are from China.
The response of the USA to a nuclear or chemical attack, even if far less deadly and destructive, would be immediately and massive. But our response to a biological attack? Destroy ourselves even further and send the attackers massive sums of money as a reward - while we are being continuously made sick, harmed and killed and our society smashed.
The most effective WMD is covert biological attack, because it can be used with only benefits for doing so, while slaughtering the enemy by every measure.
