DES MOINES, Iowa -- Donald Trump faced an all-too-clear sign of GOP divisions Friday in two Midwestern battlegrounds, embraced by party leaders in one state but ignored in another as he strained to overcome deepening concerns about his presidential candidacy.

Some of Iowa's Republican elite will appear alongside the celebrity businessman for an afternoon rally, his third appearance in the swing state over the past two weeks. But in neighbouring Wisconsin, a state Trump insists he can win, the state's best-known Republicans said they were too busy to attend his evening event.

Sen. Ron Johnson and House Speaker Paul Ryan citied scheduling conflicts, while Wisconsin Gov. Scott Walker said he'll attend an all-you-can-eat spaghetti dinner instead of appearing with his party's standard bearer.

"Welcome to Wisconsin, Mr. Trump, but let's get something straight," Wisconsin's Assembly Speaker Robin Vos wrote in an open letter to his GOP colleagues ahead of Trump's arrival. "We are Ryan Republicans here in Wisconsin, not Trump Republicans."

The tale of two states underscores Trump's mounting challenges during one of the most tumultuous weeks of his unorthodox campaign. He has skipped from one misstep to the next, sparking a fresh wave of Republican defections among longtime party loyalists who refuse to support their presidential nominee -- including some who even publicly support for Democrat Hillary Clinton.

Clinton faced tough questions of her own Friday when pressed to explain her email practices as secretary of state and why many voters distrust her.

Addressing a group of minority journalists, she insisted she "never sent or received anything that was marked classified," while again conceding it was a mistake to conduct State Department business on a private email server.

Clinton also acknowledged many people don't trust her.

"It doesn't make me feel good when people say those things, and I recognize that I have work to do," Clinton said. She added, "I'm going to work my heart out in this campaign and as president to produce results for people."

Yet Trump's gaffes have largely overshadowed Clinton's vulnerabilities as the Democrats work to recover from a bruising primary election season.

Complicating the Republican Party's 2016 challenge are fresh signs the nation's economy is strengthening under a Democratic president.

With Election Day little more than three months away, the Labor Department reported Friday that U.S. employers added a healthy 255,000 jobs in July, a sign of confidence that could point to a resilient economy. The unemployment rate remained a low 4.9 per cent as more Americans launched job searches and nearly as many were hired.

Trump's approach to national security came under fire Friday as well, with former CIA Director Michael Morell contending the Republican nominee would make "a poor, even dangerous commander in chief."

Morell, outlining his views in The New York Times, also questioned Trump's unusual praise of Russian President Vladimir Putin

"In the intelligence business, we would say that Mr. Putin had recruited Mr. Trump as an unwitting agent of the Russian Federation," wrote Morell, who served presidents in both parties over the past three decades.

Trump has done little to help himself this week.

He conceded Friday he was wrong to claim repeatedly in recent days that he saw a video of a U.S. cash payment going to Iran.

The New York billionaire has cited a $400 million payment the U.S. made to Iran this year, delivered on the same day that Iran released four American hostages. Trump charged on Thursday in vivid detail that the Iranian government released a video of the cash exchange to embarrass America.

"The plane I saw on television was the hostage plane in Geneva, Switzerland, not the plane carrying $400 million in cash going to Iran!" Trump tweeted Friday morning.

He has refused to admit any error, however, on a higher-profile dispute with an American Muslim family whose son, U.S. Army Capt. Humayun Khan, was killed in Iraq. Republican leaders and military veterans have called on Trump to apologize for criticizing the Khan family, who appeared at last week's Democratic National Convention.

Trump sparked further GOP outrage earlier in the week when he refused to endorse Ryan, a Wisconsin Republican and the party's top elected official.

Ryan has endorsed Trump, but he said in a Friday radio interview that his endorsement isn't a "blank check" and pledged to speak out against the businessman's divisive positions if necessary.

The tension between the Republican heavyweights complicates Trump's push to compete in Wisconsin, a state that hasn't voted for a Republican presidential candidate since 1984.

Like Ryan, state Assembly Speaker Vos said he's not pulling his endorsement of Trump because he believes Clinton would be worse. But Vos, too, was skipping the Trump rally on Friday.

"I have a thing," he said.

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Peoples reported in Washington. AP writer Scott Bauer in Madison, Wisconsin, Kyle Potter in St. Paul, Minnesota, Jill Colvin in Des Moines, Iowa and Lisa Lerer and Erica Werner in Washington contributed to this report.