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All of that, Western security officials fear, makes it a prime target for Russia and its leader, Vladimir Putin. Under the “Narva scenario,” NATO worries that Putin could try to claw Narva into Russia. Such a move would mimic Russia’s incursion into Crimea, a Ukrainian territory it annexed in 2014, and its efforts to sow unrest in eastern Ukraine. But a similar push into Estonia would have even farther-reaching consequences: Estonia is a member of NATO.

Such a situation would then be a test of NATO’s commitment to Article V of the Washington Treaty, the one-for-all, all-for-one provision that requires the 29 NATO members, including the United States, to come to the defense of other member states.

Article V has only been invoked once, in the aftermath of the September 11 attacks on the United States. If it were used again, this time at the request of Estonia in response to Russian aggression, would the entire alliance—crucially, the United States under President Donald Trump—come to Estonia’s aid? The New York Times reported this month that Trump has considered withdrawing from NATO, and the president has questioned the alliance’s efficacy publicly on several occasions. Remarks and reports like these are once again raising questions about his commitment to countries like Estonia, and sparking fears that he is emboldening Putin.

In 2014, when Russia invaded eastern Ukraine and swallowed Crimea, Putin painted himself as the protector of Ukraine’s Russian-speaking minority. “Millions of Russians went to bed in one country and woke up abroad,” Putin said, referring to the fall of the Soviet Union. “Overnight, they were minorities in the former Soviet republics.” Kremlin-controlled media claimed that the new government in Kiev posed an imminent threat to the Russian-speaking population in eastern Ukraine. After the invasion, Crimea held a (widely discredited) referendum in which 95 percent of the population purportedly voted to become part of Russia. Across eastern Ukraine, Russian-backed separatists continue to wreak havoc and undermine Ukraine’s sovereignty.

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Estonian defense officials I met this month in Tallinn, the capital, bristled at the notion that Narva could be the next Crimea. Estonia is not just a member of the European Union and NATO, they say; it is also far less corrupt than Ukraine, and while the average income in Narva is the lowest in Estonia, it is still almost double the level across the river, in Ivangorod, Russia.

But even as Estonian government officials dismiss concerns about Narva’s future, they are racing to further incorporate Narva into the rest of Estonia. A nationwide survey last year found that while almost 90 percent of Estonian-speaking respondents favored NATO membership, just 32 percent of Russian speakers backed Estonia being part of the alliance. The last thing the Estonian government wants is for Putin to claim to be the defender of Russian speakers in Narva, as he did in Crimea. For one month last year, Estonia’s president, Kersti Kaljulaid, took the unprecedented step of moving her office from Tallinn to Narva. To counter the influence of Russian-language media, Estonia is also pouring in development funds and using arts and culture to try to improve life here.