Hillary Clinton could spend $2.2 million every day until the Nov. 8 election without running out. And every month she widens her cash advantage over Donald Trump. As of Sept. 1, it was a $55 million gulf.

But the Democratic nominee's plans to keep up her fundraising schedule were slowed up this weekend by health concerns.

Clinton was scheduled to return to California on Monday for still more finance events, but called off plans out West for two days of fundraising, campaign events and an appearance on Ellen DeGeneres' talk show after she had to abruptly leave a 9/11 anniversary ceremony Sunday complaining she was overheated.

She had to be helped into a van before going to rest at her daughter Chelsea's home. Clinton has been diagnosed with pneumonia, put on antibiotics and advised to rest.

Her allies say future fundraising efforts could help other Democrats because the party can keep building up voter turnout operations. It would serve as protection in a rollicking race against a man who claims to be worth $10 billion and once said he was willing to spend up to $1 billion to get elected. So far, he's put about $60 million of his own money in his campaign.

Even when Clinton is busy campaigning, wallets have been flying open for her.

As she wrapped up a speech in Kansas City on Thursday night, running mate Tim Kaine was in New York entertaining five donors who'd given $500,000. A day later, Clinton was in the city telling donors, "I'm all that stands between you and the apocalypse" at a private concert headlined by Barbra Streisand.

The singer's rendition of "Send in the Clowns" tore into Trump. "Is he that rich? Maybe he's poor? 'Til he reveals his returns, who can be sure?" Streisand sang. "Who needs this clown?"

Clinton scooped up more than $4 million there, and that wasn't her only fundraiser of the day. Hours earlier, she held a far more exclusive one at the home of private equity firm executive Hamilton "Tony" James. The 30 people at his home together chipped in at least $1.5 million.

Much of the money Clinton is raising goes into efforts to find and persuade voters to back her candidacy, and get the ones who do to show up at the polls or cast their ballots early where they can. It's a costly endeavor.

Her campaign has a staff of about 700, with a monthly payroll of almost $5 million. She is spending roughly $10 million each week on television ads, according to Kantar Media's political ad tracker. She also just began leasing a Boeing 737, dubbed "Hill Force One," to travel to the most competitive states.

"If you think of an election as a conversation with voters, you have to keep having it all the way through, and that takes significant resources," said Amy Dacey, a Democratic consultant and former chief executive officer of the Democratic National Committee. "It's smart to continue to raise until the end."

Four years ago, President Barack Obama raised more than $1 billion for his re-election, a number that Clinton's national finance chairman Dennis Cheng has cited as a goal.

By the end of August, Clinton had raised about $600 million for her campaign and allied Democratic groups, an Associated Press review of campaign finance records found.

In a conference call last week with top fundraisers, Clinton's top aides urged them to go out and raise at least $100 million more by Election Day. That's in addition to the campaign's efforts to harvest small donations online and via direct-mail.

Having that money on hand will allow Clinton to quickly use resources in late-emerging contested states.

"There isn't much time left, but on the other hand, a lot can change very quickly," Dacey said. "You have to have the ability to respond."

Those who start giving at this late stage of the race do so for different reasons. Some may sense Clinton is destined for the White House and want to back a winner. They did for Obama in the closing days of his first presidential campaign.

The soon-to-be-president's campaign alone raised $153 million in September 2008, more than in the previous two months combined. Employees in Obama's Florida campaign headquarters remember mail with donor checks piling up in the office during the closing weeks of the campaign.

Other donors may worry that Trump -- who commands seemingly limitless media attention -- could overtake Clinton unless she has the cash to fight him off.

Clinton's latest fundraising solicitations highlight that fear factor. In one email last week, campaign manager Robby Mook wrote that Trump is "closing the gap in the national polls and even pulling ahead in some key states."

He continued, "There are 62 days left in this election, and if we get outworked or outspent, we're going to lose."

The email closes with a bright-red donate button.

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Associated Press writer Catherine Lucey in New York contributed to this report.

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Follow Julie Bykowicz on Twitter at: http://twitter.com/Bykowicz

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Keep track on how much Clinton and Trump are spending on television advertising, and where they're spending it, via AP's interactive ad tracker. http://elections.ap.org/content/ad-spending