Nice pledge JFK but where were the Americans in 1968 when the Soviets rolled into Czechoslovakia? Another unanswered question is "who is going to pay for this?"
We spent over $8 trillion in Afghanistan and look where that got us. The only beneficiaries were the contractors and the Taliban.
We spent over a $1 trillion in today's money in Vietnam and look where that got us.
There's a difference between getting involved with another country's internal politics and assisting another country repelling a military invasion.
We went into Iraq and Afghanistan on pretexts that were not based on fact and quite frankly went there on behalf of a Congress bought and paid for by rich folks and corporations who saw those wars as opportunities to make money.
Even then we could have accomplished something. When we first went into Afghanistan we enjoyed popular support in Afghanistan. However after a couple years of third string diplomats, as well as put troops generally looking down on them and referring to them as "a bunch of rag heads" we pretty well lost the battle on the good will front.
In Iraq we leveled the place, then made a half hearted token effort to rebuild and then left.
Compare that to the assistance we provided to both Japan and Germany after WWII. If we'd have just leveled them and went home, both would have been hot beds of instability, terrorism and on going conflict as well.
Ironically what required us to stay there and rebuild those countries was the fact that if we left the Soviets would have filled the vacuum and converted them to communist countries, like they did in East Germany.
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Vietnam was a conflict politicians were never going to let the military win, out of fears of expanding the conflict with China and Russia. We never should have gone in at all knowing we were not going in it to win it.
Similarly we meddled in South American affairs for decades trying to prop up democracies is cultures with an alcalde system where the average person really preferred a dictator, even a corrupt one, as long as things got done and they didn't have to mess with it. You can't have a democracy without a democratic tradition and that takes at least a generation to create.
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But none of that reflects the reality in Ukraine where Russia first invaded and took the Crimea in 2014 (while Obama just sat on his hands and "went high" when Putin "went low").
Trump was even worse as it's clear he was in Putin's pocket with the former KGB chief no doubt having loads of demanding evidence and video of the morally bankrupt Trump in all sorts of compromising situations.
And yet he still has followers who are firmly in the camp that we should not intervene and oppose the naked aggression by Russia in its invasion of Ukraine.
Those folks seem to forget how poorly that worked for democratic nations in the lead up to WWII when Hitler just kept taking one region or country after another.
Putin's agenda is no different. He has the end goal of reforming the entire former Soviet Union and Warsaw pact. With each success he'll become harder to stop.