Transcript for Massive Showdown Looming for the Democrats

Next tonight, the race for 2016, and a massive showdown looming for the democrats. Hillary Clinton today marching in a memorial day parade in new York, but it's the California primary, and a surging Bernie sanders that had one top supporter delivers a strong message for Clinton's opponent. This, as Donald Trump prepares to face reporters to explain just what he's done for vets. Here's ABC's Mary Bruce. Reporter: Today, a memorial day tradition. Bill and Hillary Clinton marching in their hometown parade in chappaqua, New York. I love it. I love being here. Reporter: But Bernie sanders, instead, going where the votes are, making a surprise appearance in San Francisco. California, once considered Clinton country, now a tossup. And Clinton today is announcing new events in the state, as one of her top California supporters urges sanders to face the facts. He ought to be able to read the sign posts, as well as anybody else. And if he did that, he would know that it's all but over. Reporter: Meanwhile, Donald Trump marking memorial day weekend at the rolling thunder biker rally for P.O.W.S. Do we love the bikers? Yes. Reporter: But trump sounding disappointed that the crowd on the national mall is not as big as he'd hoped. I thought this would be, like, Dr. Martin Luther king, where the people would be lined up from here all the way to the Washington monument, right? Reporter: Trump himself had five deferments to avoid serving in Vietnam. He says he's raised millions for veterans. And we just raised almost $6 million for the vets. Reporter: But trump has yet to prove it, and tonight, the questions are mounting. And trump is now holding a press conference tomorrow, hoping to put those questions to rest. He's now promising to reveal how much he's raised for veterans and where all that money went. Tom? Mary Bruce from the nation's capital. Mary, thank you.

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