Your writing sounds like some powerpoint bullet points a think thank would present to circlejerk back and forth with military brass.

> ... is cybersecurity. ...

Like, that applies to any information connected system. Do you mean defend space craft from cyber attacks or attack space craft? Either way, not so different from UAV or many other terrestrial targets is it now? Do you mean maybe that a human can't get to it in time to respond to an attack? You can't get to a remote missile silo sometimes for hours as well or other remote outposts (like many in alaska and bering sea). What is very odd about your remark is how you envision a cyberattack is superior to missiles shooting down space craft. Honestly, would love to hear about any high level attack vectors aside from radio jamming.

> The only real fully existential physical threats to the US will come not from sea, air, or land, cyber, or biology where it is already well defended, but from space.

Excuse me but have you read the news in the past few years? The internet is leading america into a civil war many expect to take place in the next decade or so. The internet is not a space domain, US cybercom exists FYI. For kinetic attacks, ICBM are sort of space based attacks since they re-enter from orbit, THAAD as crappy as it is addresses that, it is not a new concern at all. The only deterrence is possibility of a counter attack. So long as nukes from the various delivery strategies are viable it is a non-issue. Basically keep developing better ICBMs and defenses against them.

> The existence of a Space domain dilutes the integrity of a US ability to secure a physical perimeter in which it can exercise its sovereignty and from where it can project its power.

Which isn't new, reagan even tried the whole "star wars" initiative because of the concern. Are we talking about mexico and canada here? Or do you expect China to send space troopers within ICBM like vehicles along with ground invasion vehicles and supply lines? Or are we still talking about ICBMs and anti sattelite weapons? If so, better icmbs and defenses against them? Non-nuclear weapons, say a laser carrier destroyer will be bad, prevents a planned ground invasion of a remote country (which is a good thing if you ask many americans tired of foreign invasions) but will not be effective against retaliation if US soil is attacked.

To translate what you are saying in military speak (correct me if I am wrong):"it will be a lot harder to intervene in foreign nations' affairs and protect american economic interests like oil and shipping lanes if other countries get better at space based weapons" right? The security of the homeland is still a given because of the might of the Navy, and Airforce. But it does mean not being a military superpower, China will mess up most of the world and the west's global influence might dwindle? Well that is a risk but an economic and political one not one of a military invasion of the homeland by foreign powers which is the only purpose the military serves.

As for the geopoliticsl concerns, I am not saying they shouldn't be addressed but short of an actual invasion risk, the country crumbling from the inside out is a much higher concern. Vietnam and Afghanistan were lost because americans couldn't support them, military thinkers are so disconnected from americans they don't even consider this a risk. People not being able to afford a living, shelter and basic dignity is a higher risk than space craft. Politicians controlled by foreign adversaries and corrupt judges and bribery infested government are more likely to support and promote a civil war.

Although I for one vehemntly disagree and think America is still great and great days are ahead, many refused to celeberate July 4th because of the state of the nation. That is a greater concern, the enemies that are domestic not foreign.

I fear McNamara Fallacy is behind your line of thinking and military brass' [1], your metrics are not measuring the right things. Future battles will be lost because of internal strife before a weapon is fired IMO.

[1] http://mcnamarafallacy.com/