When Putin starts talking about annexing Mexico, then we have a problem. But that would never happen, because he or any other Russian leader would know that it would be a real threat to us.
I've seen some comparisons to having our head in the sand re: WWII, but the reality is that neither Germany nor Japan had even close to the resources it would take to invade North America.
Russia is not a threat to US security unless something catastrophic happens to our side of the MAD equation. The battle we can reasonably fight is on the economic side.