A United States presidential election is a gruelling test of a candidate's fitness for office, as it should be. It is the only elected office in the executive branch of the federal government, the only office with a national electorate. The President alone has a mandate to represent all the states, all the people.
Americans hold this unifying quality in high regard. Political opponents treat the presidency with decorum, overt partisanship in a president is considered beneath the dignity of the office.
Perhaps only Americans fully appreciate the scale of Republican candidate Mitt Romney's mistake this week when he dismissed "47 per cent of the people" as welfare dependants who would vote for President Obama no matter what.
"My job is not to worry about those people," he said. He was addressing an invited audience at a fund-raising event, not a public meeting.
He was talking political strategy, which is never edifying to hear, and imagined he would not be heard outside his financial backers who must have needed to be reassured they were not wasting their money.
They are going to need more re-assurance now. Mr Romney has written off nearly half the American people, "those who believe that they are entitled to healthcare, to food, to housing, to you-name-it".
To get his figure of 47 per cent he must be including every retiree and everyone using entitlements that Republicans normally distinguish from welfare and exempt from their calls for budget cuts.
He has handed golden ammunition to the Obama campaign. Not only has he reinforced its criticism of him as out of touch and indifferent to the needs of ordinary people but his sneer at those who pay no taxes is bound to renew attention on his own personal and company tax records.
Though none of this was intended for public consumption, it is remarkable that he would run such a risk today.
He was recorded on a hidden video device and the recording went out to the world on a website.
Nothing is private in an election for public office. Candidates should realise they are always and properly on trial.
Mr Romney's trial was not going well even before his remarks to the fundraiser.
His comment on the Olympic preparations when in London was memorably gauche and his stated views of Palestinians and the prospects for peace in the Middle East call into question his fitness for the office he seeks.
He is proving a disappointment in the very qualities that once seemed his strength. While he was criticised throughout the primaries for taking positions on abortion and public health care that were at variance with policies he espoused when governor of Massachusetts, he did seem to be a political professional.
He has the appearance, pedigree - his father was also a state governor and presidential candidate - and manner of one born to the role. He has been successful in business and in heading the organisation of a Winter Olympics.
These credentials could yet give him an edge if voters are sufficiently worried about the economy.
While Mr Obama has a substantial lead in polled support, his margin is negligible among those who say they are likely to vote.
Mr Romney is still in the race but now he needs to convince wary Americans he cares for them all.