Russia amasses troops on the border with Ukraine. What's Nato's response?

Much is being reported in the news about Russia amassing 20,000 troops on its border with Ukraine and Nato is speculating that Russia is preparing for an invasion of Ukraine.  Who knows the truth? I surely don't. But wouldn't it be great if Nato telegraphed what it was prepared to do to help Ukraine so that Russia and Putin would think twice about whether it was worth an invasion. I think so!