Story highlights Donald Trump's campaign chairman called Mitt Romney a "coward" on Sunday

Paul Manafort, the Trump aide, said he doesn't think Trump will be out-raised by Hillary Clinton

Washington (CNN) A top Donald Trump aide called Mitt Romney a "coward" and Romney's allies "sore losers" as he pushed back against Republican critics of the party's presumptive nominee.

Paul Manafort, Trump's campaign chairman, also insisted Sunday on ABC's "This Week" that his campaign is "not worried about fundraising" and won't be outspent by Hillary Clinton.

And he said Trump won't apologize for appearing to mock a disabled reporter in November 2015 -- footage now appearing in a pro-Clinton super PAC's anti-Trump attack ad -- saying that Trump has "already dealt with that matter. He dismissed it."

"He wasn't mocking him. And he's said that in the past. He said he was not making reference to him. And so he's dealt with that issue," Manafort said.

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