For someone who prides himself on his command of history, it's surprising Putin seems unable to see the parallels between Mariupol and Stalingrad. Then, as now, the invading dictator was obsessing with thoroughly controlling and dominating a city with a thoroughness that can only be justified by propaganda value, diverting resources that were badly needed elsewhere to keep pounding and pounding away. In the case of Stalingrad, Hitler believed it was imperative to take, hold, and crush the citybecause it was named after Stalin (just like Trump was determined to destroy anything with Obama's name or signature, whether it made sense to do so or not). In consequence, the Nazis were never able to achieve their original, critical objective--seizing the oil fields to the south, and lost an entire army to boot.
Of course, Mariopul is more strategic than Stalingrad was (no matter how the Germans tried to rationalize Hitler's obsession), but it may be another case of symbolism getting in the way of common sense. When Putin launched his initial invasion in 2004, he assumed that Kharkiv and Mariopul, both with majority Russian-speaking populations, would fall quickly, if not line the streets with rose petals to welcome him. Kharkiv rejected him outright, and in a foreshadowing of things to come (generating a huge morale boost in a very dark time), the Ukranians succeeded in driving the Russians out of Mariopul. Now every passing day without succeeding in fully conquering the city digs a deeper symbolic hole for the Russians--it will already be a hollow victory in which the valiance of the defenders will be the only propaganda win, and how long after the Red Army succeeds in subduing the steel plant--and finally starts freeing up troops for the Donbass-- before the Ukrainians launch a highly visible guerilla campaign that gives the lie to Putin's Mission Accomplished.