 Seth Moulton writes that Joe Biden has long been a mentor and friend and that he treasures the president. Whenever they met in the past, Mr Biden would break into a big wide grin and say how glad he was to see the congressman. But last month at a small gathering in France, he said the president didn't seem to recognize him. Mr Moulton, along with more than 30 other members of Congress, says Mr Biden should now step aside as the Democrats nominee.