You agreed to fund your own militaries as part of the agreement to be in NATO.

It was 'agreed' later on by the same people who support Europe being invaded, and as far as I know, it's only a guideline. Besides, there is no procedure to throw anyone out of NATO.

yet you all expect the US to step in and clean up the messes in your own back yard.

The main advantage of NATO is that it tamps down on intra-NATO wars. You don't need to do anything for that.

I will bet you would be singing a much different tune if we were to tell Russia and China that protecting Europe is no longer our problem.

Not at all. China is quite far. They're not going to invade Europe. Russia is not going to invade Europe either. Besides, we have nuclear weapons.