Democrats knew a general election battle between Hillary Clinton and Donald Trump would be rough, but many never considered the potential of a nailbiter. During a primary in which Trump usurped the GOP establishment, alienated crucial sectors of the general electorate on issues like immigration and abortion and dinged his own approval ratings, many Democrats salivated at talk of a November duel with the billionaire. Now, as Trump prepares for a general election showdown, veteran Democrats warn there is little room for complacency. "It will be close," said Mark Alderman, a veteran Democratic Party fundraiser who worked on President Barack...