I do think it’s very plausible that the tariffs are a trial balloon to see what would happen in the event of a war with China. The US is going to assess their actual level of dependence, and public resilience in face of shortages.

I’d argue the Ukraine accomplished the opposite of creating a quagmire for Russia. It absorbed a huge amount of western resources, and split unity of the west. The US is in a far weaker position as a result, both materially and economically. The main support Russia would provide for China wouldn’t be military support. China doesn’t need manpower for war, nor do they need industrial support. What they need is resources, food, and energy. Isolating Russia from the west ensured that Russia would divert these resources towards China now. Not only that, but there’s a revival of DPRK happening as well because of Ukraine. Russia has now fully resumed trade with Korea, and with that western blockade is effectively dead. DPRK now also has real experience fighting a NATO army making it one of the strongest and combat ready armies in Asia.

While there is likely some magical thinking in the US regarding technology such as missile shields, the reality is that balance has swung firmly in favor of the attacker. Both Russia and China have working hypersonic weapons, and currently there is no defense against them. The US, on the other hand, is still incapable of producing these types of weapons itself.

The whole golden shield thing is just an embezzlement vehicle. On top of all that, China just cut US off from the supply of critical rare earths which would be necessary on a massive scale to develop this program. These are essential inputs for any sort of advanced tech nowadays. China has an effective monopoly on refining many of these minerals, and there are no alternatives. Building out an industry to do it domestically would literally take decades. This is an eye opening read on the subject https://www.niocorp.com/china-launches-new-precision-strike-against-pentagon-rare-earth-supply-chains/