As Russian forces regroup for a massive battle in eastern Ukraine, Americans are wondering how to help Ukraine repel them.

My suggestion: Listen to the leaders of the tiny Baltic democracies, Estonia, Latvia, and especially Lithuania. All are NATO members whose nations border Russia and who are deeply experienced in repelling the Kremlin.

Having lived under Soviet rule, the Balts have no illusions about the need to prevent Russian President Vladimir Putin from scoring a brutal “victory” over Ukraine, something which could still happen if NATO members don’t send heavy weapons quickly. Their leaders are blunt about the long-term threat to Western nations if they fail Ukraine.

» READ MORE: Lithuanians warn from experience: don't negotiate under blackmail | Trudy Rubin

I spoke this weekend via WhatsApp to Žygimantas Pavilionis, chair of the Lithuanian parliament’s foreign affairs committee and former ambassador to the United States, who recently visited the ravaged Ukrainian town of Bucha with other European legislators. “The Russian soldiers didn’t even have armored vests,” he told me from Vilnius, Lithuania. “Some were in parade uniforms. They expected to roll right in and have a victory parade in Kyiv.”

But it was the sight of bodies piled up in mass graves that had the delegation in tears.

Lithuanians believe the only way to stop Putin’s aggression is for NATO members to be more proactive. They say Putin will move forward when he senses weakness, but halt when he is firmly confronted.

Lithuania has led the way for Europe in halting Russian gas imports. And its prime minister went to Kyiv before the war to bring Stinger missiles. Had the West started arming Ukraine much sooner, Putin might have been deterred.

The Lithuanians warn against being deterred by Putin’s saber-rattling. “We know as Russia’s neighbors that they [the Kremlin] count on your fear,” says Pavilionis. “The majority of the West is afraid of [Russia’s] nuclear weapons.” He scorns Putin’s nuclear hyperbole, including his threat to move nuclear weapons into Kaliningrad (a small piece of Russian territory on the Baltic Sea) if Sweden and Finland are admitted to NATO.

“That threat made us laugh because we knew he had those nukes in Kaliningrad already,” Pavilionis said. “The Russians will march so long as their knife cuts through meat — until they see the bone.”

The Lithuanians believe that the West must be firm in demonstrating to Putin that he cannot defeat Ukraine.

Symbolism is important. All three Baltic presidents plus the Polish president just visited the Ukrainian capital. Pavilionis would like to see the U.S. Embassy reopen in Kyiv and for President Joe Biden to go there to inspire Ukrainians.

But practical steps are also crucial. This war has laid bare the weakness of NATO defenses and manpower. Had the Ukrainians not put up an astonishing fight, Putin might have concluded he could easily take the Suwalki Gap — the 40-mile stretch of territory that is the only link between the Baltic states and other NATO countries.

The Lithuanians would like to see more NATO troops based in the Baltics, along with a substantial and permanent U.S. troop presence in their country. They are ready to provide the infrastructure.

Baltic nations also insist that NATO must grow a backbone.

NATO allies must provide Ukraine with heavy weaponry within the coming weeks — including planes and missile defenses — before it is too late to block Russia’s massive attack in eastern Ukraine. “U.S. weapons support is good, but not good enough to take back territory occupied by Russia,” Laurynas Kasčiūnas, the chairman of the Lithuanian parliament’s defense committee, told me. “The Ukrainians are fighting for Europe, for your security, too.”

“We should focus on things we can do to help Ukraine rather than things we cannot or should not do,” added Estonian Ambassador to the United States Kristjan Prikk, whom I interviewed recently when he was in Philly speaking to the World Affairs Council.

“Putin is a risk-taker but not a suicidal risk-taker. We should not let the nuclear threat deter us from doing what is right,” the ambassador said.

» READ MORE: Europe finally seeks to end Russian gas blackmail | Trudy Rubin

“If he destroys Ukraine, that will equal a Putin victory. If he comes out of this conflict by getting Ukrainian territory he did not have before [Feb. 24] and having this legitimized, then this is in some way successful. This is a situation we should avoid.”

The Estonian diplomat also warns: “If we settle again after a disastrous war without a clear sense of who is the aggressor and who is the victor, and how the aggressor should be punished, Russia will regroup, develop new capabilities. We will have considerably bigger problems in a couple of years.”

In other words, the Ukraine war — and how it plays out — will test whether Western democracies can stand up to a dictator who seeks to annex other European countries. Baltic leaders understand that the West must meet this test. Americans need to understand that, too.