WASHINGTON: Robert Gates, the former US Defence Secretary who has worked with eight presidents, today said that he has some "real" issues with the national security and foreign policy of presumptive Republican presidential nominee Donald Trump.

"I have some real issues with things he said about national security policy and some concerns. I think there are some contradictions," Gates said.

"You can't have a trade war with China and then turn around and ask them to help you on North Korea. I have no idea what his policy would be in terms of dealing with ISIS," he said when asked about the national security and foreign policy views of Trump.

Gates said that he worries about Trump's admiration for Russian President Vladimir Putin.

However, Gates said these are issues that can always change in case Trump is elected as president of the country.

"They're policy positions, so they can always change. I have seen Presidents do that more than once. I guess one of the things that makes it challenging for me is that he seems to think that he has all the answers and that he doesn't need any advice from staff or anybody else, and that he knows more about these things than anybody else, and doesn't really feel the need to surround himself with informed advisers," he was quoted as saying by the CBS.

Gates has worked with eight US presidents.

"I worked for some very different presidents of those eight. People would say, how could you work for both Barack Obama and George W Bush? And I remind them, well, I worked for Jimmy Carter and Ronald Reagan," he said.

"The difference is, each one of those presidents, as strong-minded as each of them was, understood he did not have all the answers, and surrounded himself with experienced, thoughtful people who would give good advice, and they were willing to listen," Gates said.

They would often make their own "independent" judgments. They often would act contrary to the advice they were receiving. But, nonetheless, they only acted after they had listened to different points of view and then had the opportunity to make up their mind, he said

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