Republican Donald Trump has backed away from comments calling President Barack Obama and Democratic nominee Hillary Clinton the founders of the militant group Islamic State.
The Republican Party, meanwhile, has sought to project unity behind their candidate.
A new poll showed Mr Trump, whose unfiltered speaking style has repeatedly landed him in hot water, losing ground in three crucial states ahead of the November 8 general election against Ms Clinton.
In a surprise appearance, Republican National Committee chairman Reince Priebus, who in private expressed fury over some of Trump's actions this month, introduced the candidate at a campaign event in Erie, Pennsylvania, and the two hugged onstage.
"We're so honoured to be working with Donald Trump and the campaign," Mr Priebus told thousands of Mr Trump supporters.
"And don't believe the garbage you read. Let me tell you something. Donald Trump, the Republican Party, all of you, we're going to put him in the White House and save this country together."
Republican sources earlier said Mr Priebus was furious over Mr Trump's failure to endorse House of Representatives Speaker Paul Ryan and his feud with the parents of a Muslim American soldier killed in Iraq. Mr Trump did endorse Mr Ryan a few days later.
Mr Trump on Friday told the rally his remarks this week calling Mr Obama and Ms Clinton the founders of ISIS, as Islamic State is also known, had been sarcastic.
"I said Obama is the founder of ISIS. The founder! And these dishonest media people, they're the most dishonest people," Mr Trump said.
"So I said the founder of ISIS, obviously a big sarcastic, but not that sarcastic to be honest with you," he added.
Mr Trump first made the unfounded claim on Wednesday and repeated it through the week, including in an interview on Thursday with radio talk show host Hugh Hewitt.
"I meant he's (Obama) the founder of ISIS. I do. He was the most valuable player," Mr Trump said, adding that Ms Clinton also deserved the MVP award.
Mr Trump claimed sarcasm in July as well after he was heavily criticised for inviting Russia to dig up tens of thousands of "missing" emails from Ms Clinton's time as US secretary of state.
A Wall Street Journal/NBC News/Marist poll released on Friday suggested support for Mr Trump was eroding among voters in three battleground states.
Such states are hotly contested because their populations can swing either to Republicans or Democrats and thus play a decisive role in presidential elections, which are ultimately decided by the state-by-state tally of the Electoral College.
The poll found Ms Clinton widening her lead in Colorado, Virginia and North Carolina, while holding her advantage in Florida.
Mr Trump scheduled a speech in Warren, Ohio, on Monday that will focus on how he would handle the threat posed by Islamic State. Mr Trump has said he would "knock the hell out of ISIS", without offering details, and would persuade Gulf states to bankroll safe zones for Syrian refugees so they would not have to be brought to the United States.
Nearly one-fifth of registered Republicans now want Mr Trump to drop out of the race for the White House, according to a Reuters/Ipsos poll released on Wednesday.