Russia has attacked Georgia militarily. Russia has cyberattacked Estonia, then Ukraine. They’ve attack Ukraine militarily and annexed Crimea. Then they made their move on Kiev. We stood in their way this time. Russia has openly talked about reclaiming Estonia and Poland. Putin will never stop his conquest as long as he’s able. Standing for Ukraine has more to do with our national interest than anything else, more than human rights of the Ukranians even.
Afghanistan no longer fit our national security and national interest goals. That’s the short answer.
You don't make promises to allies and not keep them. That's going to make it very difficult in the future to get locals to assist us.
There's a huge difference between Russia and the WWII Germany. Germany had a huge industrial base as well as allies. Russia has neither if you're talking what countries would help them invade NATO. Almost a billion people and exponentially more industry verses a country of about 140 million with low life expectancy, limited industry, a poor education system. It's not the Soviet Union.
And as much as you would hate to admit it Putin never attempted to invade Ukraine while Trump was president. If he's crazy enough to attack NATO it'll be because of weak leadership on our side. Appeasement never works. Look at what's currently going on with Iran to see that.