The kingmaker in Britain's drama-soaked election faces what must be an agonizing choice.
Nick Clegg of the Liberal Democrats must decide whether to join the Conservatives, who as the first-place finishers claim a moral mandate to govern, or the defeated Labour Party, which is dangling the prize of major electoral reform that would benefit Clegg's party for years.
It may come down to a question of following head or heart.
Common sense may suggest that giving backing to the party that won by far the most votes in the election — yet fell short of an outright majority of parliament seats — would be the best reflection of the will of the people.
But the Liberal Democrats' deepest political instincts are more aligned with Labour, and the promise of overhauling an electoral system that has suppressed his party's number of seats may be a temptation that will prove too difficult to resist.
"If you ask Liberal Democrat voters who they'd prefer to see the Liberal Democrats in coalition with, it is usually about 2-to-1, Labour to Conservative," said Andrew Hawkins, chairman of polling firm ComRes.
For now, however, the party rank and file appear to be giving the leadership the benefit of the doubt as they negotiate with both big parties: A survey of hundreds of party members by the grass roots website Lib Dem Voice found a huge majority open to talks with the Tories — but 80 percent thought electoral reform should be the red line in any deal.
Meanwhile, there is a sense of urgency, a feeling that Britain needs a swift resolution and a stable government to tackle a huge public debt that imperils not only the British economy but, as recent market contagion has shown, perhaps the global recovery itself.
Clegg's party debated its choice for a fifth day Tuesday, having already extracted astonishing concessions from its larger rivals.
In a late gambit Monday, after Prime Minister Gordon Brown of the Labour Party made a surprise bid to win over Clegg with a vow to step down, the Tories promised a referendum on electoral reform — but only in a watered-down form that would do little to help the Liberal Democrats win more seats.
Labour has suggested it is willing to go farther than the Conservatives toward the type of proportional representation that Clegg's party has long lobbied for. In such a system, parties would be allocated seats according to their share of the popular vote.
Under the current system, the Liberal Democrats won just 9 percent of the seats in Parliament after gaining 23 percent of the vote.
A Liberal Democrat alliance with the Conservatives holds greater promise of stability, however.
Combining the Tories' 306 seats with Clegg's 57 in the 650-seat House of Commons would command majority support and stand a good chance of remaining in power for a full term.
By contrast, Labour and the Liberal Democrats together would fall just short of a majority and would need the support of smaller parties to pass legislation.
But the Liberal Democrats, whose leader Clegg was once a member of the European parliament, tend to be wary of the Conservatives' Euroskeptic views, and question how much leader David Cameron has truly modernized the old right-wing Tory party.
"Is it best for the country to have a rabidly anti-European party in power?" said Paddy Ashdown, a former Liberal Democrat leader and one of the party's elder statesmen.
"We may have to stomach that in the interests of the nation, but you have on the one hand the question of stability and the other the question of what is the program that is best for the country," Ashdown told BBC radio. "These are difficult decisions."
Clegg said Tuesday he was "as impatient as anybody else to get on with this, to resolve matters one way or another," as his negotiating team held further talks with Labour.
Senior Liberal Democrats said the decision would be difficult, and some party faithful were bound to be unhappy whatever the outcome.
"I think there are big internal divisions in the party," said Lembit Opik, a former Liberal Democrat lawmaker who last week lost his seat in Wales to a Conservative after having served since 1997. "With the best will in the world, Nick is going to have angry members."