'Ronald Reagan would be ashamed': Clinton campaign slams Donald Trump's controversial NATO suggestions

Hillary Clinton's campaign slammed Donald Trump's suggestion that the US violate its agreement to automatically come to the protection of NATO allies if one of them were to be attacked.

In an interview published by the New York Times Wednesday night, the Republican nominee suggested that if a small NATO country was attacked by Russia on his watch, he would not defend it if it has not "fulfilled their obligations to us."

Originally formed as a bulwark against Russia in 1949, the underpinning of the NATO alliance stipulates that an attack on one nation is an attack on all, warranting a military response from all 28 member states.

In a statement on Thursday morning, Clinton Senior Policy Advisor Jake Sullivan skewered Trump's response, saying that past NATO proponents like President Ronald Reagan would be horrified by Trump's suggestion.

"Ronald Reagan would be ashamed. Harry Truman would be ashamed," Sullivan said.

He added: "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."

This isn't the first time Trump has expressed skepticism about NATO.

In an interview with Bloomberg earlier in the campaign, Trump suggested that the NATO alliance "may be obsolete."

"NATO was set up a long time ago, many, many years ago. Things are different now," Trump said. "We're paying too much."

Trump's criticism of NATO is rooted in the fact that following the end of the Cold War, some member nations began failing to spend 2% of their annual GDP on defense, a requirement to remain in NATO. However, with an increasingly aggressive Russia, some key member states have upped their defense spending at the urging of the Obama administration.

Experts argue that the outsized American role in NATO allows the US to maintain outsize influence over the vision and direction of NATO operations.

Throughout the campaign, Trump has regularly expressed skepticism with longtime strategic partnerships with other nations, claiming that the US takes on too much military burden with Western Europe and countries like Japan and South Korea.

The Republican presidential nominee has floated the idea of countries like Japan becoming nuclear powers in order to defend themselves from attack.

"Maybe they would be better off - including with nukes, yes, including with nukes," Trump said on "Fox News Sunday" in April.