ABC's chief White House correspondent, Jonathan Karl, says Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE's initial decision to not reveal she was suffering from pneumonia was "borderline deception."

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Appearing on ABC Monday, Karl predicted that polls asking about Clinton's trustworthiness would take a big hit after the medical episode on Sunday in New York that has led to widespread speculation about her overall health.

"This is her biggest vulnerability as a presidential candidate, that voters simply do not trust her," Karl said. "Those are remarkable numbers for both candidates. You have roughly a third saying they trust her. Two-thirds suggesting not."

A recent ABC News/Washington Post poll showed 35 percent of Americans find the Democratic presidential nominee honest and trustworthy. Only 31 percent in the same poll find her opponent, Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE, honest and trustworthy.

"If you can't trust her about how she feels, what can you trust her about?" Karl asked. "This was not simply a lack of transparency yesterday, this was borderline deception."

Karl then blasted the campaign for its lack of candor with the public.

"They said simply that she was overheated. They said that she was feeling fine. Then you find out she had been diagnosed with pneumonia," Karl said.

"Not a good day on the transparency front."

The Clinton campaign said the 68-year-old candidate will be resting for the next two days instead of flying to fundraising events in California.