Opinion editor's note: Editorials represent the opinions of the Star Tribune Editorial Board, which operates independently from the newsroom.

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It's fitting that the last stand by a few thousand Ukrainian forces in Mariupol is at the Azovstal Iron and Steel Works. Iron and steel, after all, are two fitting descriptions of Ukrainians, who successfully repelled Russian troops from most of the western portion of their country.

And yet despite the intrepid, patriotic pledge to fight to the end, Ukrainian forces are estimated to be outnumbered in the key port city by a six-to-one margin. That means that Russian troops may take Mariupol, which they've already nearly ruined through ruthless bombardment and other killing that's claimed more than 20,000 citizens in what surely are war crimes. (Another 100,00 citizens remain trapped without water, food or heat by the Russian siege.)

If Mariupol falls, it would be the first significant tactical victory, however sordid, for the invading Russians. It may solidify the Kremlin's revised goal of seizing an eastern, resource-rich portion of Ukraine that generally stretches from Kharkiv in the northeast (which has also endured Russian shelling) to Mariupol in the southeast and beyond, perhaps making possible a land bridge to Crimea, the portion of Ukraine that Russia illegally annexed in 2014.

This revisionist vision of its war objectives doesn't mean that portions of western Ukraine weren't destroyed and aren't still under attack. In fact, on Monday a Russian missile attack on Lviv, a major departure point for desperate refugees fleeing to Europe and beyond, killed seven people, the first casualties in that city during the war. It was part of a barrage of what Russia claimed were more than 300 strikes, still mostly in the east, as it prepares for its major offensive.

"This will be a tougher battle for Ukraine to fight than the first major offensive, because the first major offensive was based on unrealistic expectations about Ukraine resistance," John Herbst, former U.S. ambassador to Ukraine, told an editorial writer. Herbst, who's now senior director of the Atlantic Council's Eurasia Center, added that Russia "probably learned that was a mistake" and that the more relatively open terrain may favor Russia in this next phase of the war.

But even though as Russia had unrealistic expectations about Ukrainian resistance, Kyiv and allies in NATO national capitals should not make unreasonable assumptions about Russian President Vladimir Putin's endgame, which Herbst said "still remains the subjugation of Ukraine." The next "six or eight weeks" may be focused on the east, but Herbst believes that Russia "will still be coming back for a much bigger bite after that; the long-term goals have not changed."

The West's long-term goals also shouldn't change: a stable, peaceful Europe and a Ukraine free to choose its geopolitical direction. While it's likely that Eastern Europe in particular will be threatened by Putin, it cannot become vulnerable to him, which means doing everything possible to support Ukraine's brave resistance.

To date, President Joe Biden has been diplomatically and rhetorically resolute, rightfully accusing Russia of war crimes and even genocide. Militarily, a significant amount of money and materiel (including a recent $800 million commitment) — but not troops — have come from the West, in particular the United States.

The continued military aid is laudable and must continue. But the U.S. in particular needs to make sure the aid is sufficient, and Herbst has his doubts. "So, the policy gets better over time, but in relatively small increments, and it's always not quite up to the challenge at the moment," he said.

It's understandable and appropriate that neither Biden nor any other Western leader wants their nation or the NATO alliance to directly fight a nuclear-armed Russia, but they must not allow Putin to intimidate them out of a response that will give Ukraine the best fighting chance — one they've proved again and again that they've earned, including by showing their mettle in a Mariupol steel plant.