GETTY The presidential candidate says his commitment to NATO will depend on the commitment of other states

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His decision on whether to come to the aid of allies would be based on whether those nations "have fulfilled their obligations to us". Under the NATO treaty, allies are bound to come to the aid of any member under attack. But asked about potential Russian aggression towards the Baltic states, the Republican said if Moscow attacked, he would weigh up their contribution to the pact before deciding on whether to their aid.

He added: "If they fulfil their obligations to us, the answer is yes."

If they fulfil their obligations to us, the answer is yes Donald Trump

Trump was quoted as saying he would force allies to shoulder defence costs he say the US has borne for decades, cancel long-standing treaties he views as unfavourable, and redefine what it means to be a partner of the US. "I would prefer to be able to continue" existing agreements, he said, but only if allies stopped taking advantage of what he called an era of American largess, the New York Times wrote.

NATO training exercises Wed, June 8, 2016 The North Atlantic Treaty Organization, also called the North Atlantic Alliance, is an intergovernmental military alliance based on the North Atlantic Treaty Play slideshow AFP/Getty Images 1 of 26 Polish troops land with parachutes at the military compound near Torun, central Poland as part of the NATO Anaconda-16 military exercise

Democratic presidential candidate Hillary Clinton's senior foreign policy adviser, Jake Sullivan, said in a statement: "Trump has apparently decided that America lacks the moral authority to advance our interests and values around the world." Trump has for months raised questions about the money the United States pours into NATO, which he says needs to be re-configured to take account of today's global threats. His America First rhetoric has raised alarm in allied countries that still rely on the US for protection.

FLYNET Trump has made it clear he is not happy with the amount of money the US puts into NATO

The phrase "America First" was used in the 1930s by isolationists who sought to keep the United States out of the Second World War. Trump was quoted as saying that if elected, he would not exert pressure on Turkey or other authoritarian allies about purging political opponents or cracking down on civil liberties. He said the United States has to "fix our own mess" before trying to sway the behaviour of other nations.

FLYNET The presidential hopeful thinks the US needs to solve its own problems, before it helps others