Story highlights Sources say Donald Trump is frustrating advisers

The Republican nominee veered off message in recent days

(CNN) Donald Trump aides and people close to his campaign are increasingly frustrated by his insistence on waging various fights that steer him off message.

Sources close to the campaign are describing a series of missteps that are trailing the GOP presidential nominee, most prominently his now multi-day battle against Khizr Khan, the Muslim father of a killed US soldier.

Trump has spent the days since the Democratic convention litigating whether their son is a hero, and on Tuesday only moved onto an equally unhelpful news cycle: whether he supports House Speaker Paul Ryan, and the 2008 presidential nominee, John McCain, in their primaries.

A knowledgeable Republican source told CNN that some of Trump's campaign staff -- even campaign manager Paul Manafort -- "feel like they are wasting their time," given Trump's recent comments. And two sources close to the Trump campaign said privately they wished Trump would apologize to the Gold Star family, even though the Khans attacked Trump from the stage at the Democratic National Convention last month.

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