Meghan McCain, the daughter of now-deceased US senator John McCain, has found herself the online target of Bernie Sanders’s supporters after a tweet in which she apparently questioned his physical fitness for office.

After Sanders narrowly won the New Hampshire primary, McCain tweeted: “Democrats really gonna nominate a 78 year old white socialist who recently had a heart attack? Really......”

Her tweet drew an immediate response from Sanders’ supporters, including the more outspoken and dedicated fans often known as “Bernie bros”.

Some who responded to McCain’s tweet pointed out that her father ran for president at the age of 72 after a bout of cancer, and that ageists expressed the same concerns about him then that she is voicing about Sanders now.

Some of the tweets, however, veered into vitriol and even graphic threats of violence.

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Others on the left not usually classified as “Bernie bros” also joined in the pile-on. In one of the more civil responses, former Democratic presidential contender and spiritual author Marianne Williamson replied to McCain to draw a comparison with Donald Trump.

“Better than a 73-year-old would-be autocrat who displays no morals, shows constant disrespect for the traditions of our democracy, and seems to have no heart at all”, she wrote. McCain replied to her with “OK boomer”.

An hour later, she responded to the Sanders fans’ reaction: “Bernie supporters responding with the calm nuance they are known for to my slight criticism tonight. Ya’all sure live up to your “Bernie bro” reputation, don’t ya?”

But the criticism continued: “Please explain to me exactly how one would respond with nuance to a criticism that asks an ageist question in a condescending way...you failchild,” read one tweet.

McCain is now known for being a co-presenter of TV show The View, where she represents a mainstream conservative point of view relative to the other more liberal hosts.