(AP) -- Donald Trump's presidential bid has thrived on controversy of his own making. Now, the Republican nominee kicks off the first full week of the general election campaign having put his strategy of saying the politically unimaginable to its greatest test yet.

Trump broke a major American political and societal taboo over the weekend when he engaged in an emotionally-charged feud with Khizr and Ghazala Khan, the bereaved parents of a decorated Muslim Army captain killed by a suicide bomber in Iraq. He further stoked outrage by implying Ghazala Khan did not speak while standing alongside her husband at last week's Democratic convention because they are Muslim.

The outcry was swift and bipartisan, leaving Trump largely isolated among his fellow Republicans and potentially putting at risk whatever progress the New Yorker had made during his convention at winning over the independent voters who will likely decide the fall election.

"I am appalled that Donald Trump would disparage them and that he had the gall to compare his own sacrifices to those of a Gold Star family," said New Hampshire Sen. Kelly Ayotte, a Republican seeking re-election in one of the nation's most competitive Senate contests.

Both House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell issued statements praising Capt. Humayun Khan, awarded a Bronze Star and a Purple Heart after the U.S. soldier was killed in Iraq in 2004. Though neither explicitly mentioned Trump, the congressional leaders pointedly denounced his proposed ban on foreign Muslims entering the country, a policy he had altered in recent weeks but nevertheless one that returned to the center of the campaign debate via his attacks on the Khan family.

For the second time in a week, Trump's running mate, Indiana Gov. Mike Pence, issued a statement that appeared designed to put some space between the two men atop the GOP ticket. The father of a Marine, Pence said Sunday that he and Trump believe Capt. Khan is a hero and his family "should be cherished by every American."

Last week, Pence said Russia would face "serious consequences" for meddling in U.S. elections at roughly the same time Trump appeared to encourage it, telling reporters he would welcome Russia unearthing emails that Democratic nominee Hillary Clinton deleted from the private servers she used while secretary of state.

Pence's late Sunday statement came after an afternoon of debate among his aides as to whether he should find a way to subtly distance himself from Trump's comments, according to a person familiar with the internal campaign conversations who spoke on condition of anonymity because they were not authorized to discuss them publicly.

At last week's Democratic convention, the Pakistan-born Khizr Khan told his son's story, questioned whether Trump had ever read the Constitution and said "you have sacrificed nothing." During the speech, Ghazala Khan stood quietly by his side.

Trump responded in an interview with ABC's "This Week," saying: "If you look at his wife, she was standing there. She had nothing to say. She probably, maybe she wasn't allowed to have anything to say."

Ghazala Khan wrote in Sunday's Washington Post that she did not speak because talking about her son's death remains difficult. "Every day, whenever I pray, I have to pray for him, and I cry. The place that emptied will always be empty," she wrote.

Trump's dispute with the Khans entangled his campaign in a days-long dispute at a moment when voters typically begin paying closer attention to the presidential race. Trump tried several times to deflect the criticism, though he refused to back down from his initial attack.

"Am I not allowed to respond?" Trump tweeted on Sunday morning. "Hillary voted for the Iraq war, not me!" His tweet followed a late Saturday night statement where Trump described Humayun Khan as "a hero," but said his father had "no right" to "say many other inaccurate things."

That doesn't matter, said Wisconsin Gov. Scott Walker, who enthusiastically endorsed Trump at the Republican convention. He said Sunday that as the parents of a fallen solider, the Khans are off limits.

"I don't care what they say. You'll never hear me question anything about a Gold Star family," Walker said. "I've gone to too many funerals, met too many families. What they've sacrificed is just unbelievable."

Trump was taken aback by the uproar, believing he was attacked first by Khan, according to a person familiar with the candidate's thinking who spoke on condition of anonymity because they were not authorized to speak publicly about private conversations.

The billionaire real estate mogul has also told people around him that when answering questions on "This Week" about sacrifice, he was simply pointing out his own and not equating them to those of the Khan family, the person said.

Trump spokesman Jason Miller said Sunday a biased media was at work framing the issue as one of "Trump vs. Khan" and suggested the real issue was a "Trump vs. Clinton" battle over fighting terrorism. He added that Clinton camp's was fanning the controversy to distract from her weaknesses on national security, highlighted by the investigation into her private email server.

Clinton carefully leapt on Trump's comments over the weekend, even as her aides admitted that they weren't sure whether the dispute would spark a significant movement of Republicans to her campaign. Their immediate goal is to keep Trump enmeshed in a fight against the Khans.

"One doesn't know where the bottom is. It's hard to imagine anyone who has ever run to be president of the United States saying any of what he's said," Clinton said, at a campaign stop in Ashland, Ohio.

She told Republicans: "This is a time to pick country over party."

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Associated Press writer Steve Peoples in Colorado and Catherine Lucey in Iowa contributed to this report.

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