In the very beginning of this war, I actually convinced an aged marxist acquaintance of mine to overcome is knee-jerk pro-Russia reaction exactly by pointing out that the Russian invasion of Ukraine was wrong for the same reasons as the US invasion of Iraq was wrong and thus if one was trully a person on Principles, one would judge the actions of Russia now just like the actions of the US were judged back then.
It helps that, as I don't do mindless tribalism, I feel not compulsion whatsoever to judge some nation more leniently than other, and could just point out the question of principle (the strong attacking the weak to take their stuff using made up self-serving excuses) with no hypocrisy as I've been pretty consistent in judging actions by their own merits and demerits independently of who is doing the deed.
Anyways, the point being that IMHO the lefties who remainin tankies by now are the ones either in a thick closed bubble of ideas and who thus never get things presented to them like this by other lefties or the ones who are little more than ideological parrots with a below average intelligence.
Because community matters to many people more than ideological consistency, and some far-left groups have made a community culture that involves knee-jerk opposition to 'Western' polities in all circumstances. "US bad, therefore, Russia good." Or rather, "Critical support for Putin's genocides." See: Hexbear, Lemmygrad
The guy was a leftwinger during his young years when Portugal was under the yolk of a Fascist Dictatorship, so his relationship with Marxism and Communism was first of the heart and then of the mind.
Of course the Russia as he was taught to believe it was when he was a young revolutionary (the Beacon of Hope for leftwingers who were under the yolk of Fascism, not the Stalinist shithole), occupies a warm place in his hearth and when the bond is emotional it's normal for it to not simply flip On and Off depending on who governs that country.
Mind you, this is a guy who didn't join the Portuguese Communist Party (which was definitelly a tool of the Soviet Union) because he thought it was too top-down authoritarian and instead joined a different, smaller, party that wanted Communism but without the authoritarianism, so he definitelly was and is more than an unthinking tribalist parrot, which is probably why he could be convinced by simply reducing the subject to a question of principle.