Putin and Xi's big advantage over the US is that American presidents get elected every 4 years. If they gradually encroach on their neighbors and make intervention unpopular in the US via propaganda they don't need to attack a US base.

The other big issue is US adventurism in Iraq (and to a lesser extent Afghanistan) has made US citizens wary of any international actions, no matter the details. It's especially galling how many of the same people who were cheering on the direct military conquering of Iraq are now against supporting Ukraine at an arms length. "Can't get fooled again", indeed.