Though the office of deputy prime minister is relatively new in British politics, and though there have been stretches since 1945 when British governments haven’t even featured a deputy prime minister, Nick Clegg risks becoming the first sitting deputy prime minister to lose his constituency in the United Kingdom’s general election on Thursday.

Throughout the campaign, Clegg has struggled to take a clear polling lead in Sheffield Hallam in south Yorkshire. His party, the Liberal Democrats, are predicted to lose up to half of their 56 seats in the House of Commons, and Clegg’s surprisingly tough race means that his future as an MP is just as fragile as his future as the leader of the Liberal Democrats, which joined a formal coalition with the Conservatives following the May 2010 general election. In that campaign, Clegg stole the spotlight in the country’s televised leader’s debates against both current prime minister David Cameron and then-prime minister Gordon Brown.

This time around, Clegg has been forced into an awkward mix of defending his record in government while attacking Cameron’s Tories for going too far in cutting social services in the party’s zeal to reduce the country’s budget deficit. Clegg’s popularity collapsed early in the coalition, when he not only agreed to budget cuts in the midst of a recession, but particularly after he consented to an increase in tuition fees from around $3,000 to around $9,000, backtracking on what had been a key LibDem pledge in the 2010 election. A groveling apology to LibDem voters only made things worse for Clegg.

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A Lord Ashcroft poll released April 29 showed Clegg losing to Labour’s Oliver Coppard by a 1% margin. A Guardian/ICM poll released May 4, however, indicates that Tory voters are voting tactically for Clegg in a bid to retain his seat. The Liberal Democrats have historically been somewhat left of center, most importantly opposing British participation in the US-led invasion and occupation of Iraq in the 2000s and creeping civil liberties abuses by Labour. Clegg, with a market-friendly, traditional economically liberal perspective, is still seen as the most likely LibDem leader to bring his party into another coalition with the Conservatives after May 7.

In contrast, if Clegg loses his seat and the party is forced to choose a new leader quickly, the favorite would be the secretary of state for business, Vincent Cable, whose views on economic policy lie much closer to Labour’s than to the Conservatives.

Even as Clegg signals that Cameron’s promise of a 2017 referendum on British membership in the European Union need not be a deal-breaker for a coalition, he’s said that his party could partner with either major party, adding ‘a heart to a Conservative government and a brain to a Labour one.’ 

If Clegg survives, and he takes the Liberal Democrats into a fresh coalition with the Tories, his party could be expected to slow the impact of Conservative plans for aggressive cuts in a second term to reduce further the budget deficit, which is currently 5% of GDP, and it would also push for more funding for education and the National Health Service, while blocking Conservative plans to cut public sector pay as a way of slashing government spending.

Increasingly, however, the likelihood that the Scottish National Party (SNP) will hold the balance of power, and the SNP leadership’s refusal to support Cameron, means that Labour will form the next government, even if it wins fewer seats than the Conservatives. In that case, the Liberal Democrats could back Ed Miliband as prime minister, thereby reducing Miliband’s reliance, however informal, on Scottish nationalists. It’s an option that Labour leaders are increasingly discussing, with neither Labour nor the Conservatives likely to win close to the majority they’ll need for a government. Whether either Miliband, Clegg or Cable admit it, a ‘Lib-Lab’ coalition would give Miliband much greater credibility in the eyes of British voters. Despite Cable’s more progressive leanings, most business leaders would prefer his as chancellor to Labour’s shadow chancellor Ed Balls.

The last time the two parties joined up in Westminster was in 1977, when prime minister James Callaghan briefly formed an informal arrangement with what was then the Liberal Party, though it lasted only through September 1978, nine months before the Conservatives, under Margaret Thatcher, took power. More recently, however, a Lib-Lab coalition governed Scotland shortly after devolution took effect between 1999 and 2007.

Even a much-reduced Liberal Democratic caucus is still expected to be at the heart of negotiations. Despite polling at just 8%, the party will win over 20 more seats than the United Kingdom Independence Party (UKIP), even as UKIP wins 10% to 15% of the vote nationally.

The tight race is most stunning because in 2010, Clegg won the district easily with 53.4% of the vote, with the Tories taking just 23.5% and Labour just 16.1%. Even before Clegg won the seat for the first time in 2005, it had become one of the reliable constituencies for the Liberal Democrats.