I'm no immigration lawyer - just a greencard holder who's been through a couple of adventures in the process. There's a decent summary here:

http://lawandborder.com/risk-abandoning-green-card-abroad-6-...

Key things: 6 months absence can be a factor in challenging your status as a Lawful Permanent Resident. 12 months absence means your green card (the actual document) is no longer valid for re-entry but it doesn't automatically make you a non-LPR.

Customs and Border Patrol can deny you entry, as we've just seen, on the basis executive action, legally questionable or not. But they can't take away your LPR status - only an order from an immigration court judge can do that.

A lot of this is cold comfort to any LPR caught up in this and unable to re-enter right now - but there is a process and the status itself is not so trivial to take away. The call to help organizations who provide legal aid to such people (and refugees and other visa holders) seems like the right thing to me, it's probably the most immediate need.

You're right, even as I wrote the original comment I knew in the back of my head that "lose their green card" wasn't the right way to put it; I just wrote carelessly. Thanks!

I'll true it up for you, it is actually worse than you describe.

If you are absent > 6 months you could end up with your green card status listed as 'abandoned', but even if you come back every 6 months that is no guarantee at all that it will not be listed abandoned.

The golden rule seems to be to be more than 6 months per year in the USA, preferably substantially more than 6 months to avoid ambiguity.

Green card is for people who want to immigrate into US; US isn't interested in granting citizenship to people living elsewhere (never was), the stated goal is to diversify US population. Given that, such a requirement makes sense - and is very common in immigration procedures around the world.

The rules to naturalize are separate and more stringent than the rules to maintain the green card. Talking about granting citizenship is a separate issue.

Further, it appears that after a year your green card is by statute no longer valid for reentry into the country. You don't lose the green card, but your reentry has to be special-cased by CBP or a consulate.