Yves Herman / Reuters

On April 4, 1949, Johannes Kaiv, the acting consul general of Estonia’s government-in-exile, sent a letter to Secretary of State Dean Acheson, which read:

I have the honor to offer my best wishes to the signatories of the North Atlantic Pact, and to express my confidence that they, inspired by the ideals of democracy, of individual liberty, and the rule of law, will strive relentlessly for peace with justice, which excludes peace at any price. Therefore, I express the belief that countries which were forcibly deprived of self-government and independence will benefit by this noble endeavor.

Estonia would have to wait 55 years to join NATO, a decade after the nation regained its freedom from the Soviet empire. But the values that make NATO relevant today are the same that Kaiv identified in 1949, when he lamented the fate of his occupied homeland. As we celebrate the 70th anniversary of this historic alliance, we must remember what is at stake: protecting democracy, individual liberty, and the rule of law.

In 2014, Russia invaded Ukraine, illegally annexed Crimea, and supported armed proxies that continue to occupy a part of eastern Ukraine to this day. According to the United Nations, 13,000 Ukrainians have died, with as many as 30,000 wounded, as a result of Russian-backed aggression in Ukraine.

Had Estonia not been a member of NATO in 2014, would it have shared Ukraine’s tragic fate? We doubt that the residents of Tallinn—or Vilnius, Riga, Warsaw, Prague, or Budapest, for that matter—would ever want to test that proposition.

After the attacks of September 11, 2001, our NATO allies did more than signal their support for us. They invoked Article 5, the provision of the treaty supporting the principle of collective defense, for the first—and, so far, only—time in the history of the alliance. They joined us on the battlefields of Afghanistan to bring those responsible for that heinous attack against the United States and the American people to justice. They partnered with us for the past two decades on counterterrorism and security operations throughout the world. More than 1,000 men and women from our allied partners gave their lives in this conflict for our freedoms. The United States Congress and the American people will never forget their sacrifice.

This is why more than three in five Americans view NATO favorably. This is why we are leading an effort in the Senate to pass legislation that would require the consent of two-thirds of the United States Senate for any present or future president of the United States to be able to exit NATO.

In an alliance as broad as NATO—with its 29 members, 21 partners for peace, and an additional 15 nations engaged in formal programs—there will always be differences. For instance, some of Turkey’s recent actions have raised serious questions regarding Ankara’s intentions and commitments to certain fundamental democratic principles, such as human rights and press freedoms. Yet we must seek to resolve these differences within the alliance, not outside of it.

For long-term sustainability, it will be important for all NATO members to increase their spending on defense, in order to meet and exceed the minimum threshold of 2 percent of GDP. We strongly believe that as allies, we should have frank but respectful conversations about this important issue.

NATO should also devote more resources to the challenge of hybrid warfare, including protecting our cyberspace and countering information operations that seek to damage our democratic systems. NATO should also become more global and use both its Partnership for Peace program and its formal dialogues around the world to grow beyond its North Atlantic focus.

As Winston Churchill famously said: “There is only one thing worse than fighting with allies, and that is fighting without them.”

This is why we will always stand with NATO.

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