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Presumptive Republican presidential nominee Donald Trump is facing challenges as he attempts to unify the GOP.

Spokespersons for former presidents George H.W. Bush and George W. Bush have said that the Bushes won't be endorsing Trump or commenting on the presidential campaign.

Additionally, Mitt Romney, the party's 2012 nominee, has no plans to attend this July's Republican National Convention, where Trump is expected to be officially nominated.

Former George W. Bush speechwriter Marc Thiessen said on "The Real Story" this afternoon that he's not surprised by the Bushes decision because of the offensive statements Trump has made on the campaign trail.

Thiessen pointed out that Trump has accused George W. Bush of knowing about the 9/11 attacks beforehand and lying about WMDs in Iraq in order to drag the U.S. into a war in the Middle East.

"You're not going to get the Bush endorsement if you say those kinds of things," Thiessen stated.

Meantime, Romney has been one of Trump's harshest, most outspoken critics, so it's not particularly surprising that he won't attend the convention in Cleveland.

Watch more above.

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