Andrea Leadsom's Conservative colleagues are "appalled" by her comments on motherhood, ITV News' Libby Wiener says.
One backbencher has told ITV News that Leadsom's suggestion that being a mother gave her an advantage over her childless rival Theresa May was "vile".
Another said she should consider her position and withdraw from the race to decide the next Tory leader and prime minister.
Duncan Smith told Peston on Sunday that there had been "a black-ops" operation to destroy her reputation.
Leadsom's suggestion that being a mother would make her a better prime minister has sparked an almighty row - read exactly what she said.
A major row has erupted after Andrea Leadsom allegedly said being a mother makes her a better choice for prime minister than Theresa May.