You are going to see scare articles like this one claiming SecDef Austin will send US troops to fight Russia if Congress doesn't come up with more $$ for Ukraine. This sort of half-truth is why I seldom cite Gateway Pundit articles.
Ukraine wants to defend their territory, and they grind down the Russian military in the process. We help them pay for the effort. That is win-win.
What Austin actually told Congress is that if we fail to aid Ukraine and Russia consequently wins there, we can expect a Russian attack on a NATO ally sometime soon. "Soon" defined as after, or perhaps before, Russia gobbles up whatever non-NATO tidbits remain in Europe (Georgia, Moldova, Armenia).
Austin's reasoning - transparent and hard to argue with - is that as long as Ukraine keeps the Russian military tied up in Ukraine they don't have the depth necessary to launch another major offensive elsewhere on a NATO ally.
When a NATO ally is attacked we are treaty-bound to fight their attacker, presumably Russia. At that point American GIs will fight Russians. Austin is correct, his is no empty threat.