First: Hillary would have to step down. To the best of my knowledge, once nominated, a candidate cannot be "fired." For instance, Bob Dole had a rough start to

First: Hillary would have to step down. To the best of my knowledge, once nominated, a candidate cannot be "fired." For instance, Bob Dole had a rough start to his 1996 presidential campaign, and the republican party decided to cut their losses and pull support. They couldn't remove Dole, and he wouldn't step down. That meant that they just refused to fund him or promote his candidacy, and focused their efforts on congressional races. The strategy worked well for the republican party, but Dole seems (understandably) bitter about being left high and dry by his own party. Note that no living US president has endorsed Trump, and George H.W. Bush has said that he plans to vote for Hillary. Bob Dole is the closest thing Trump has to a presidential endorsement. Remember when there was talk of the republican party cutting support for Trump and focusing on congressional races? I won't pretend to know what Bob Dole thinks, but I suspect that his own history factors into why he supports Trump. Second: Yes, it would make it easier for Trump to win. The ballots have already been printed in most states, and early voting has begun in some areas. Some number of people have already voted for Hillary. If Hillary is removed from the ticket and another Democrat is selected, Hillary's votes probably wouldn't be transferred. I can't imagine it's legal to switch someone's vote after-the-fact. Needless to say, you don't get to vote a second time just because your candidate stepped down. Meanwhile, in some areas they wouldn't be able to (for either time or budgetary constraints) print new ballots. That means Hillary would still be on the ballot in some areas, and it would be up to voters to write in the name of the new democratic nominee.