Clinton is resisting that tide. She accuses President Bush of slighting allies and emphasising arms over diplomacy. But, with an eye on next November, she also refused to apologise for her vote authorising force against Saddam Hussein, led the Democrats in acknowledging that Americans will remain militarily engaged in Iraq after 2008, and supported the hard-line resolution on Iran. Toughness is her lodestar.

In all these ways, the candidates are targeting different Democratic parties. Clinton’s bread-and-butter domestic agenda and muscular internationalism match the inclinations of the blue-collar voters and seniors at her coalition’s core. Obama’s collaborative foreign policy and somewhat nouvelle domestic policy capture the priorities of his base, voters with more education and fewer economic needs.

Democrats will need both sets of voters to recapture the White House — which means that, for all their tension today, if Obama or Hillary Clinton captures the nomination, the winner will need to learn from the loser before this marathon ends.