i try to model the geopolitics of today, including the domestic situation, on some period of the late roman republic.
when put on that frame, it becomes clear very quickly that the reason the dominant faction in the US (which still has not fully consolidated power though they are able to be pretty open about it now) is picking and escalating a fight with a russia is to achieve an end that secures their grip on power domestically, even if it costs them a portion of the country in the process. as we know, the major issue for the at present is the november elections, so impacting that event is the target.
as long as they win, it is worth it to them.