No, it is not the unwillingness to call out infractions. It is more the extreme disproportionality of liberals. The invasion of Ukraine is such a historical evil that any explanation of it (outlawing of Russian in school and government documents, being worried about NATO expansion, etc.) is excusing the Putin Regime that does evil only because they like evil and have no other motivation than maximizing evil. So any Russian that isn't currently attempting to overthrow the government is an evil orc that deserves death.
But all of the wars of aggression and invasions the US made in the 21st century means that the US is slightly flawed and being too left or wanting to overthrow the government is too far. We need to hold our nose and vote for Democrats because they might make the invasions slightly more limited and be more polite while funding the Israeli genocide.
But that is actually the real issue that Liberals take issue with. Explaining that there are motivations beyond Putin being evil and that all of the US's wars of aggression makes it the worst state in the current world, rather than a flawed and imperfect democracy that should still be the model for the world is what makes one a tankie.