Yes, he really should be worried about it. I wrote about Trump’s mortal fear of getting dementia because he watched his father deteriorate with Alzheimer’s disease because he watched his father mentally deteriorate with Alzheimer’s disease. In today’s Washington Post (gift link) they tackle that subject in depth: Donald Trump invited his extended family to Mar-a-Lago in the mid-1990s. As the clan gathered at the palatial Florida estate, though, his father was badly struggling, according to Mary L. Trump, Donald’s niece. Fred Trump Sr., the pugnacious developer then in his late 80s, didn’t recognize two of his children at the party, recalled Mary L. Trump, who attended the gathering. And when he did recognize Donald, the family patriarch approached his son with a picture of a Cadillac that he wanted to buy — as if he needed his son’s permission. The incident, Mary L. Trump said, left Donald Trump visibly upset at his father’s descent into dementia, which medical records show had been diagnosed several years earlier.Trump reflected his anguish in an interview around that time, with Playboy in 1997 reporting that seeing his father “addled with Alzheimer’s” had left him wondering “out loud about the senselessness of life.” “Turning 50 does make you think about mortality, or immortality, or whatever,” Trump, who had recently reached that milestone, told the magazine. “It does hit you.” Today, as the 77-year-old Trump seeks to return to the White House, he is still focused on the ravages of dementia — but this time…