'What Are You Afraid of?' Sanders Asks After Trump Backs Out of Debate Trump blames Democratic Party's "rigged" system and television networks.

 -- Donald Trump backed down from much-hyped proposed debate that he earlier said he wanted to have with Sen. Bernie Sanders.

Trump, who has now secured enough delegates to clinch the Republican nomination, said in a statement released today, "Now that I am the presumptive nominee, it seems inappropriate that I would debate the second-place finisher." Sanders said he wanted the debate to happen.

Trump reiterated his claim that "the Democratic nominating process is totally rigged" and that "crooked Hillary Clinton and Deborah Wasserman Schultz will not allow Bernie Sanders to win," referring to the Democratic National Committee chairwoman.

Neither Clinton nor Sanders has enough delegates to win at this point.

The prospect of a debate originated from a question Sanders submitted to Jimmy Kimmel before Trump's appearance on the late night talk show Wednesday. At a press conference in North Dakota on Thursday, Trump was asked about it and said that money from the event should be raised "for maybe women's health issues or something."

Now Trump is stepping back and taking the more traditional approach of waiting for the Democrats to nominate a candidate.

"I will wait to debate the first-place finisher in the Democratic Party, probably crooked Hillary Clinton, or whoever it may be," he said in the statement.

Sanders learned about Trump’s decision to back away from the debate when asked about it at a Los Angeles event.

“I heard that he was going to debate me, and then I heard that he was not going to debate me ... Mr. Trump is known to change his mind many times in a day,” Sanders said.

“Trump goes around — he’s a bully, he’s a big tough guy. Well, Mr. Trump, what are you afraid of?” said Sanders.