David Axelrod, who is a CNN political commentator, tweeted, "Antibiotics can take care of pneumonia. What's the cure for an unhealthy penchant for privacy that repeatedly creates unnecessary problems?"
The veteran Democratic strategist was referencing a rough 48-hour stretch for the Clinton campaign over the weekend, during which Clinton was forced to leave a September 11, 2001, terrorist attack memorial service after "overheating," which her team later revealed was the result of a pneumonia diagnosis the former Secretary of State, who is 68, had received on Friday but which had not been made public at the time.
Donald Trump's campaign manager Kellyanne Conway piggybacked on Axelrod's criticism, replying to his tweet: "Wow. Well said."
Clinton's communications director, Jennifer Palmieri, responded on Twitter, "We could have done better yesterday, but it is a fact that public knows more about HRC than any nominee in history."
She added, "In contrast to HRC, Trump has been less transparent than any nominee in modern history."
Conway shot back at Palmieri: "D-E-F-E-N-S-E. Yet, Jen has a point: they know enough about Hillary that they don't like her, don't trust her."
Axelrod -- who helped run both of Obama's successful presidential campaigns, including his primary fight with Clinton in 2008 -- has been an intermittent critic and backseat driver during Clinton's 2016 campaign.
In February this year, during a difficult stretch for the Clinton campaign due to revelations about Clinton's email use at the State Department, Axelrod cryptically wrote on Twitter:
"When the exact same problems crop up in separate campaigns, with different staff, at what point do the principals say, "Hey, maybe it's US?"
During the Democratic primary, he also criticized Clinton's team for overthinking their debate strategy, which had been detailed in a New York Times report.
"Kind of bewildering as to why @HillaryClinton folks are so explicitly, if anonymously, laying out her debate strategy a week out. #justdoit"