Theresa May is still on course to be prime minister but it is worth remembering that in 2015 the Conservatives beat Labour by seven points in the popular vote and any lead less than that represents a swing away from them to Labour.
A dead heat in votes, for example, would still leave the Tories as easily the largest party but nearly 30 seats short of an overall majority.
With the Conservatives having mopped up the southern half of the country in the past two elections their focus has turned to Labour-held constituencies further north and in Wales.
Many of these seats attracted high Ukip support in 2015 and a big “leave” majority at last year’s European Union referendum. If the Tories could win over the bulk of those voters, an increased majority would be assured.
Ukip is not fielding a candidate in 17 of the 41 constituencies where Labour has a majority of less than 10 points over the Tories but a switch to the Conservatives is not clear-cut.
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Seats in northern England such as Wakefield may not after all drop into the Tory lap for the first time in decades. Even seats lost to Labour in 2015 such as Dewsbury and Lancaster and Fleetwood may prove difficult targets.
In Wales, too, Conservative optimism has waned. An early poll suggesting the Tories could win the majority of Welsh seats for the first time in more than a century was countered by Labour’s better than expected local election performance.
In London, a “remain” stronghold, Labour gained seven seats in 2015 and any further drift in this direction would make it hard for the Conservatives to regain the four seats they lost last time, including Ilford North. The Tories must also defend their own majority of 165 votes in Croydon Central.
The Liberal Democrats will believe that any revival is most likely to bear fruit against the Conservatives in clear “remain”-voting constituencies such as Twickenham.
Whatever happens on Thursday, if Labour cannot return to its once-dominant position in Scotland it is hard to see how it could assemble enough MPs to come close to being able to form a majority government.
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The Scottish National Party carried all before it in 2015, but the Conservatives failed by only 328 votes to win Berwickshire, Roxburgh and Selkirk and could stage a revival in northeast Scotland.
Professors Colin Rallings and Michael Thrasher are directors of the Elections Centre at Plymouth University