We are halfway through the election campaign and the Conservatives lead Labour by roughly 10-12 points. The lessons learned from the 2017 fiasco have been applied, and a more disciplined and focused campaign has produced a lead at half-time which is … exactly the same as the lead Theresa May held at the same point last time. Yet half-time in this race feels very different to the 2017 midpoint. What has changed?

Trajectories matter. In 2017, May’s was already firmly downward – a lead that peaked at over 20 points soon after the election was called had already been cut in half by this point. A botched manifesto launch, arguments over the “dementia tax” social care proposals and May’s poor performances on the campaign trail had combined to produce a sense of crisis. Conservative polling this time has followed a gentle upward trajectory, like a well-executed jumbo jet takeoff. The campaign has featured the usual smattering of gaffes, wobbles and awkward encounters with angry voters, but nothing serious enough to blow things off course (yet).

This isn’t just about campaign “momentum”. Several things really are breaking the Conservatives’ way. Nigel Farage’s decision to stand down Brexit party candidates in Conservative-held seats has given Boris Johnson a headstart in the race to squeeze third-party support, removing a competitor for Leave voters from the board in nearly half the country’s constituencies, and signalling to Leave voters everywhere that Johnson’s Brexit policy is tacitly endorsed by Farage himself. The Conservatives have gained nearly three points in polling since the announcement, while the Brexit party has fallen by a similar amount.

Further Conservative advantages emerge when we dig beneath the headline polling figures. Johnson holds a massive lead over Jeremy Corbyn in favourability ratings and “best prime minister” questions; while Corbyn’s ratings have ticked upward slightly since the campaign started, there is no sign yet of the dramatic surge he received in 2017. Labour’s image has worsened with voters: it is seen as less competent, more divided, more extreme than it was at this point in the last campaign.

The public is also more focused on Brexit than they were in the last election, an important advantage given that the other major issues on voters’ agendas – the NHS, education and the environment – are ones that typically favour Labour. And while Leave voters are fast uniting behind the Conservatives, Remain voters are still split. Labour has picked up some ground since the campaign started, but they still win less than half of the Remain vote. Labour Leave voters are switching to the Conservatives in much larger numbers than Conservative Remain voters are going to Labour, a difference that could prove decisive in the Leave-leaning marginals that may decide this election. A constituency poll last week from Great Grimsby, a Labour held marginal that voted 70% Leave in 2016, showed the Conservatives 13 points ahead.

So the Conservative leadership will be happy with the state of thingsat the halfway stage. But there is still a long way to go. The same polls that give the Conservatives healthy leads also give them reasons to worry: more voters than ever before think they may change their minds before polling day, and record numbers say they are personally invested in who wins the election. Although Johnson personally is preferred to Corbyn by a large margin, ratings of the Conservative government are very negative, with particularly dismal scores on public services and immigration. The radical spending promises in last week’s Labour manifesto could still mobilise discontent with austerity on the one hand, while the radical cuts to immigration promised in the Brexit party “contract with the people” could yet attract voters angry at the Conservatives’ past failed pledges on migration control. Even if policy appeals don’t capture the public imagination, the growing threat of a dominant Conservative majority could yet focus the minds of Remainers and tribally anti-Tory voters, and convince them to unite behind the Labour banner.

Events beyond the government’s control could also shake the campaign. The final weeks of the 2017 contest were overshadowed by terror attacks, which Labour framed as evidence that Conservative austerity was putting national security at risk. We cannot know what twists remain in the road this time. The Tory campaign has already been wrong-footed by flooding, and could be thrown off course again by another bout of extreme winter weather. With A&E waiting times at an all-time high, a major NHS winter crisis remains a real possibility.

The Conservatives’ lead is also more fragile than it looks. With DUP bridges burned, there will be no other parties willing to back a Johnson administration in the Commons. The vagaries of the electoral system leave the Conservatives needing a lead of seven points or more to be confident of a majority, and it is majority or bust this time. A two or three-point swing to Labour would therefore be enough to put everything up for grabs once again.

In the run-up to the 1997 election, Roy Jenkins compared Tony Blair’s approach to the campaign to a museum curator carrying a priceless Ming vase across a slippery floor. The electoral Ming vase is now in the hands of the much clumsier Boris Johnson, and he still has a lot of obstacle-strewn ground to cover.

Rob Ford is professor of politics at the University of Manchester