resident Biden forgot that he was speaking in Midtown Manhattan Wednesday and instead welcomed world leaders to Washington — making his latest staggering gaffe after being forced to end his campaign for a second term due to Democratic concerns about his mental acuity. “Thank you, thank you, thank you. Welcome to Washington,” Biden, 81, said at the InterContinental New York Barclay hotel about five minutes’ walk north of the iconic Chrysler Building. Biden launched into his speech without missing a beat, suggesting he did not know he made the mistake. “Fellow leaders, friends, for 944 days [Russian President Vladimir} Putin...