David A. Andelman, editor emeritus of World Policy Journal and member of the board of contributors of USA Today, is the author of " A Shattered Peace: Versailles 1919 and the Price We Pay Today ." Follow him on Twitter @DavidAndelman . The views expressed in this commentary are his own.

(CNN) There are few more vulnerable spots along NATO's entire perimeter than the Suwalki Gap , an about 60-mile stretch of territory and a critical rail line separating Poland from Lithuania, linking Russian Kaliningrad with Putin's staunch ally Belarus. If Vladimir Putin takes comfort in NATO's waffling, or doubts US willingness to spring to the defense of the Baltic republics, it's here any shootout between NATO and Russia could start. Or even World War III.

Vice President Biden paid an urgent trip to neighboring Latvia in August to meet the presidents of all three Baltic states -- Estonia, Latvia and Lithuania -- to assure them that "we have pledged our sacred honor ... to the NATO treaty and Article 5," which says an attack on one NATO ally is an attack on all. And all three Baltics are firm members and believers in NATO. But Biden continued: "You occasionally hear something from a presidential candidate. It's nothing that should be taken seriously, because I don't think he understands what Article 5 is."

Donald Trump's suggestion the United States might not come to the aid of every NATO nation that's attacked unless they contribute more toward NATO has raised questions over America's commitment here. This is, of course, an insane precondition to place on backing a region so devotedly pro-American. Yet the fear is that win or lose, Trump and all he represents may leave a dangerous aftertaste long after the ballots have been counted.

"We have been a neighbor of Russia not for 100 years but 1,000 years," said Marju Lauristin, Estonia's member of the European Parliament and a quarter-century ago one of those who helped free her nation from the Soviet Union. "But Russia is looking only at Americans. So we are following very closely the debate in America to see what is happening in our part of the world."

Until the present political campaign, the United States had given few suggestions of anything but a total commitment to the three free states of the Baltics. Indeed, throughout World War II and Russian occupation, the Baltic nations' flags were present in the Hall of Flags at the entrance to the State Department in Washington.

This is only right; it is imperative that America sees the defense of these democratic nations as a pillar of its international posture going forward. In practical terms, this could mean returning American missiles to the region, and extending the US presence beyond the "tripwire" troops that now rotate through , and that the Baltics must settle for. After all, these three nations are likely Putin's next target. But whatever happens, we cannot allow a repeat of what happened from the mid-1940s to 1953, when Lithuanian partisans fought a desperate rear-guard action in the forests and swamps of their nation, hoping desperately for the arrival of American troops to join them, as US broadcasts had pledged.

Unfortunately, Russia has made significant moves of it own, with the arrival in Kaliningrad of a battery of intermediate-range Iskander-M missiles , with a range of more than 300 miles and the capacity of carrying nuclear warheads across the Baltics and into Poland -- itself an apparent violation of the intermediate range nuclear forces treaty. The Russian Baltic fleet is also a regular presence, its most advanced fighter jets buzzing American ships and reportedly violating Estonian and Finnish airspace.

Meanwhile, Poland, another NATO member, is still awaiting deployment of a missile shield -- a promise by George W. Bush that was scrapped by President Barack Obama when a thaw with Russia was still an American goal. Now, Poland wants to revive such a project on its own dime (actually about 50 billion dimes) by installing eight Patriot missile defense systems , provided Washington approves. It must do so.

NATO's countermoves are portrayed by Western diplomats as significant: a force of 800 British troops with drones and some Challenger tanks into Estonia next spring , a rotating company of American troops (about 300 soldiers) in Lithuania.

But Russia's moves into this region are far more robust and deeper, in military and propaganda terms. Significant Russian minorities in all three countries are hardly immune. "The budget of Russia Today [TV] is 40 times that of VOA," said Zygimantas Pavilionis, longtime Lithuanian ambassador to the United States and now shadow foreign minister in the new Lithuanian parliament, who tried to help former House Speaker John Boehner understand the challenge. "When you live 100% immersed in propaganda, the majority start to believe it is true."

At dinner one evening in the Dominic restaurant in Tallinn, two Russian-speaking Estonians at the next table, a cancer surgeon and a businessman, explained why they admired Vladimir Putin. "He is strong, and he never tells us anything but the truth."

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But at the Riga Conference in Latvia a short time later, Andrei Sannikov, a Belarusian dissident now living in exile in Poland, had a different take on the threat. He was talking about the Russian troop transports that cross the Suwalki Gap regularly and the fear expressed by many Baltic leaders that they could suddenly stop and Russian troops could quietly disembark to test NATO and Baltic mettle. "I am not worried," he smiled thinly. "They will just take one look around them and defect."

But while the clear advantages of the prosperity brought by a democratic capitalism that has taken strong roots in all three of the Baltics is a powerful attraction, there remains an overarching fear that two decades of such progress could be snuffed in an instant by six divisions of Russian armor. Only a persuasive and consistent American determination could serve as a meaningful deterrent.