(CNN) -

A weekend of stumbles has Hillary Clinton suddenly looking vulnerable at a pivotal moment of her battle with Donald Trump.

Her swoon Sunday at muggy Ground Zero -- and damaging video of Clinton lurching into the arms of her security detail -- dramatically turned the state of her health from conservative conspiracy theory into a genuine campaign issue.

The episode also exacerbates questions about transparency that have long dogged Clinton's White House bid after the campaign revealed the Democratic nominee is suffering from pneumonia -- a fact it kept quiet since Friday.

But Sunday's drama was just merely a capstone on Clinton's rough 48 hours.

Clinton aides spent Saturday cleaning up her remark that "half" of Trump's supporters were "deplorables," meaning racists, sexists and homophobes. The remark, for which she later expressed "regret," suddenly united a Republican Party that has struggled to get behind its divisive nominee.

The double blows came at just the wrong time for the 68-year-old Clinton, as Trump closes in the polls and pressure builds ahead of the first presidential debate in two weeks -- an event shaping up to be a potentially pivotal moment of the campaign.

Whether Clinton's rocky weekend will turn out to be just another unexpected twist in an election season that has had everything, or exert a lasting political impact will only become clear in the coming days. She canceled a trip to California scheduled for Monday and Tuesday, though attendees of one of Monday's events were told that Clinton would appear via teleconference. The speed of her recovery and the way her enemies handle the episode will do much to shape how voters respond to her health issue.

Weekend on defense

But a weekend on defense and a possibly reduced schedule going forward threatens to slow Clinton's campaign at an unwelcome moment and will do little to calm increasingly jittery Democrats who only weeks ago were speculating about the possibility of an electoral landslide.

Donna Brazile, the interim chair of the Democratic National Committee, released a reassuring statement late Sunday wishing Clinton a "speedy recovery."

"I look forward to seeing her back out on the campaign trail and continuing on the path to victory," she said.

It was bad enough for Clinton that she had to leave the ceremony marking the 15th anniversary of the September 11 attacks early -- setting off alarm bells among her traveling press pool. But the later emergence of video showing her wobbly, staggering and stumbling before being helped into her black van conjured up the kind of image, played over and over on television, that campaign strategists dread.

The footage was more than a blow to her dignity. It will be used by opponents to validate a months-long campaign of rumors and innuendo about the true state of Clinton's health.

Trump has frequently cast doubt on Clinton's physical fitness, saying she lacks "stamina" and takes naps in the afternoon and runs on an easy schedule -- a claim debunked by reporters who follow her campaign.

His initial response to Sunday's incident was relatively muted. When asked by Fox News on Monday about Clinton's health, Trump said doesn't know what's wrong with the Democratic nominee but that he hopes her health improves.

"I really just don't know. I hope she gets well soon," Trump told Fox News, adding later, "Something is going on but I just hope she gets well and gets back on the trail, and we'll be seeing her at the debate."

Aware of potential impact

The Clinton campaign was clearly aware of the potential impact of the video. After resting at her daughter Chelsea's apartment, the Democratic nominee emerged smiling, and under her own power in front of the cameras, taking a picture with a young girl before climbing into her motorcade.

She told reporters she was "feeling great" and parried further questions by commenting that it was a "beautiful day in New York."

The campaign also tried to foster an air of normality by saying that Clinton spent time playing with her grandchildren while at her daughter's home.

But hours of speculation and uncertainty about what happened to Clinton and a lack of information about her status triggered an air of crisis.

When details about her condition finally emerged -- in the form of a statement issued through the campaign by Clinton's physician Lisa Bardack -- they only added to impressions that the campaign abhors transparency.

Trump, whose Twitter account is normally on hair trigger alert, was unusually quiet Sunday. The Republican nominee had pledged not to campaign on the anniversary of the terror attacks but his uncharacteristic silence kept the focus on Clinton all day.

Sources involved in the Trump campaign said they wanted to be respectful of the health issue. Staff and campaign surrogates were instructed not to post anything negative on social media.

Given that Trump is 70 and would be the oldest person to take the oath of office as President for a first term, and Clinton would be the second oldest, both candidates are certain to face pressure for a more comprehensive accounting of their health.