President George W. Bush will leave a "strong and positive legacy" in Asian security and his successor will maintain American engagement in the region, US Defence Secretary Robert Gates said Saturday."Actually I think this will be an area where there will be a strong and positive legacy in the future," he told a high-level security forum in Singapore six months before the US presidential elections."Any speculation in the region about the United States losing interest in Asia strikes me as either preposterous, or disingenuous, or both," said Gates, who will visit Thailand and South Korea after Singapore.