Most voters believe Joe Biden's disastrous debate performance on Thursday was not caused by a cold or too much preparation, but by dementia. That is one of the most damning findings in an exclusive national poll for DailyMail.com. Only 10 percent of respondents accepted the White House's excuse that a cold was to blame for the President struggling to answer questions or hold his train of thought during a 90-minute showdown with Donald Trump. At the same time, it reveals that Trump, 78, has extended his lead over 81-year-old Biden to six points, deepening the crisis facing the president's reelection...