Hilary Clinton led a panel discussion at Swansea University discussing adversity faced by women, where she highlighted the "intimidation" faced by female politicians.
Mrs Clinton, whose grandparents were Welsh, led a panel entitled 'Gutsy Welsh Women' where she criticised the "heavily misogynistic" atmosphere online. She said this has led to female parliamentary candidates announce they would not standing in the General Election.
The former US secretary of state also claimed social media culture was serving the "amplification of hatred" which she said led to the "political assassination" of Labour MP Jo Cox.
She said: "Unfortunately, the atmosphere online is heavily misogynistic because apparently the people, and it's predominantly, though not exclusively, men who spend their time going after women of prominence in whatever field they are in and just can't let it go.
"And it's really particular to them. Threats of death and terrible attacks, including going after their families, in particular mentioning their children."
Mrs Clinton said she had met with an unnamed female politician who had decided she was not going to stand for the December 12 General Election, who told her, "I just can't take it".
"It is a terrible loss and a loss to democracy if anybody is intimidated out of running, and disproportionately the people choosing not to run in the first instance or for re-election are women."
Mrs Clinton called President Donald Trump a "24/7 bully" when saying the public could not leave the issue of intimidation to politicians.
She told the audience: "We had an explosion of bullying in American schools, and you know... much of it is inspired by the behaviour of our president, who is a, as you know, 24/7 bully on all kinds of issues.
"That is the highest office in our land and that is the role model of our children. The children are picking up on those cues."
Asked if discussing the issues made her want a return to politics, Mrs Clinton said: "No, but it makes me more determined to support women like those on this panel and to speak out."