The only time NATO’s mutual-defense provision was invoked was after the 9/11 attacks, when European nations rallied to the US.

Trump’s eagerness to blame America’s problems on others—immigrants, competitive rivals—extends to allies, who he argues are driving up US defense spending. In the past, that had extended to merely promising to review defense agreements, but this is the first time Trump has said he would not follow treaty obligations in the event of an invasion. That obsession may play well with the base, but it doesn’t gibe with his arguments that Obama has weakened the US military.

The move also does nothing to dispel Trump’s coziness with Russia. Trump has repeatedly praised Russian leader Vladimir Putin. His campaign chairman, Paul Manafort, is a long-time confidant of Russian-backed strongmen. Last week, the Republican platform was altered at Trump’s behest to remove strong language defending Ukraine, which is facing a civil war against Russian-backed separatists.

“Ronald Reagan would be ashamed,” Jake Sullivan, Hillary Clinton’s national security adviser, told reporters. “Harry Truman would be ashamed. Republicans, Democrats and Independents who help build NATO into the most successful military alliance in history would all come to the same conclusion: Donald Trump is temperamentally unfit and fundamentally ill-prepared to be our Commander in Chief.”

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