Trump was asked about the NATO alliance. He repeated his criticism that the other members of the 28-nation defense alliance do not pay their fair share.
"We pay approximately 73% of the cost of NATO, that's a lot of money to protect other people," he said.
The US actually only pays about 22% of NATO's operational budget; member states' contributions to NATO's organizational budget is proportionate to their respective gross national income. But the NATO budget only funds the civil budget, military budget and the Security Investment Program. This is a relatively small portion of national defense spending by all the countries, with the entire budget being slightly more than $2 billion. The US contribution to NATO's direct funding is less than 1% of the US defense budget.
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Trump is likely referring to the US share of defense spending among NATO countries -- that number is indeed 73%. The imbalance is due in part to the fact that only five NATO members meet the NATO recommendation that each country spend 2% of its GDP on defense, and the US GDP is significantly larger than all the other NATO members.
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NATO's official statement on indirect funding says, "This does not mean that the United States covers 73% of the costs involved in the operational running of NATO as an organization, including its headquarters in Brussels and its subordinate military commands, but it does mean that there is an over-reliance by the Alliance as a whole on the United States for the provision of essential capabilities, including for instance, in regard to intelligence, surveillance and reconnaissance; air-to-air refueling; ballistic missile defense; and airborne electronic warfare."
Because Trump says the phrase "73% of the cost of NATO" in his comments, and because that number does not reflect actual US direct spending on the alliance, and because the number captures US defense spending not-related to NATO, this is an inaccurate description of the cost of NATO.
Verdict: False.
http://www.cnn.com/2016/09/26/politics/fact-check-presidential-debate/
PS: Sanders made the same claim in one of his debates with Clinton, and has been against NATO for some time: http://www.politifact.com/truth-o-meter/statements/2016/apr/19/bernie-s/sanders-oversimplifies-us-share-NATO/
= new reply since forum marked as read
. I basically watch only PBS NewsHour and read several newspapers (NYT, WaPo, and less so my local paper). And of course read a number of solid Internet sites (Vox, TPM). I wouldn't have known anything about NATO membership without having had it reported at the time. So I know I heard it. 
