You will be alright as a green-card holder applying to med schools. I was in a similar position as you many years ago (for college applications).
On a side note, it is VERY difficult to "revoke" a permanent residency and you need major legal cause. And from my understanding, the only legal "cause" is if you physically live outside of the country majority of the time or if you commit a very serious crime (think selling state secrets or hacking into government facilities). Immigration policies, even if they are ever-changing in today's political climate, shouldn't and won't affect permanent residents (especially cause you have had it for a while!) significantly. Becoming a permanent resident of the United States is already a very difficult thing to do. There is a reason why they are granted out in 10-year terms and the renewal process is essentially just a fee lol. The step up from that to citizenship is relatively straight-forward and obviously permanent.