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ANY visitor to the Cameron home was struck by how central their disabled son Ivan and his needs were in the life of a busy household.
His wheelchair was the reason for the wide spaces in the hall and a floor downstairs was set aside for his room and team of carers. Everything from the routine of moving between London and his Oxfordshire constituency and how to plan for holidays that could include Ivan, but not hold back the family life of the other two children, was a matter of what David Cameron once called, "advanced logistics".
The health of a child stricken by severe cerebral palsy has determined the pattern of their lives since his birth six years ago.
Only parents of children with similar conditions will fully identify with the strains and emotional burdens that has placed on them: the 24-hour care, fear of any unusual symptoms or fits, the midnight hospital dashes and the ultimate dread of sudden loss.
Ivan had been seriously ill before and there were at least two major scares. The serious epilepsy which accompanied the condition made the risk of a fatality ever-present - Mr Cameron spoke of taking life "one day at a time" and knowing that his son would not live to an old age.
The reality is always different. Samantha Cameron told friends the family had enjoyed its first proper Christmas break without a dash to hospital and with Ivan in reasonably good health: a memory we can only hope is of some comfort now.
She found her own way to combine the roles of political wife and businesswoman with a home life which always looked cheerful and well-tempered, but was run like clockwork to ensure time with her children.
However personal, these things have a political angle. Mr Cameron's smooth demeanour, protean politics and privileged background would have made him a less attractive electoral proposition were it not for the softening impact of his son's illness. The real tenderness he showed his son often left more of an impact on his visitors than any number of carefully prepared arguments and charm offensives.
Of course, the Camerons' situation is not the same as so many others who struggle to combine care of a seriously ill child with family life and work. But it gave the boy who breezed from an upper class background to Eton and Oxford to television PR and Conservative Central Office an insight into what it feels like when life does not roll along smoothly.
Gordon Brown, who lost his daughter shortly after birth in 2001 and has a son with cystic fibrosis, took the emotionally intelligent step of cancelling Prime Minister's questions and the unveiling of the Thatcher portrait today. He has no relationship to speak of with Mr Cameron, but this is a time for cessation of hostilities.
