(1) No one knows the future.
(2) Leaders, like the rest of us, do not always act/react rationally. Why did Hitler declare war on the US? .
(3) Little things - back-and-forth -- can lead to big things that no one wanted. This is how WWI started.
(4) The US has been the pre-eminent world power for the last 75 years. This is changing. China is on the way up, we are on the way down. And we are rotting from the inside. This reality means that there is a very good chance of war between the two sides.
(5) There are other tensions in the world, not directly involving the US, between nuclear-armed powers, or powers allied to nuclear-armed powers.
--- Israel (and the Sunni Arab states) vs Iran.
--- Japan and China
--- Armenia and Azerbaijan
--- Albanians and Serbs in Kosovo [another blessing of diversity]
--- India and China
--- India and Pakistan
And of course Ukraine, where we have finally succeeded, after 30 years, into goading the Bear to lash out.
(6) We all are subject to 'normalcy bias'. We discount the probability of unpleasant events in the future, and engage in linear projection from the present: today was like yesterday which was like the day before yesterday which was.... therefore ...
[
Normalcy bias - Wikipedia ]
Therefore ... it is simple common-sense prudence to believe that the US should prepare for a big war -- not necessarily directly against the US, at least not at first.
With what weapons this war might be fought -- nuclear, biological, EMPs, and who knows what else they've been cooking up -- is not predictable.
Radioactive fallout can come down far from a conflict zone. Biological warfare vectors can spread beyond their intended target.
This means that the US should initiate a nation-wide 'Civil Defense Preparedness' campaign.
We could learn from the Chinese, Swiss and Israelis about making our buildings into safe(r) havens, and in other things too.
State and local government should have plans for dealing with a range of serious emergencies.
And individuals should prepare as well. For example, if you have children/grandchildren, you should get a couple of bottles of potassium iodide, which protects thyroid glands from the cancer-causing effects of radioactive Iodine-131.
There are a number of other things individuals should do as well, but they deserve a separate thread.
(This really should not be a Left vs Right issue, although I suppose extreme partisans on either side would want to dissuade their political opponents from taking any precautions. A massive government-directed Civil Defense Preparedness campaign would, of course, encourge 'preppers', who are mainly rightwingers. On the other hand, it would involve a lot of government spending. So we're quits.)