After Britain has its general election, the next question is likely to be whether there is another referendum on Scottish independence. Following First Minister of Scotland Nicola Sturgeon’s recent call for a second referendum, further constitutional crisis in Britain is a matter of when, not if. It was only in 2014 that Scotland voted to remain in the United Kingdom by a 55-45 percent vote. The referendum was described by the Scottish Nationalist Party (SNP) as “once-in-a-lifetime” event. So, what has changed?

The short answer is, of course, Brexit. For the SNP, this constituted a “material change” of sufficient magnitude to warrant a second attempt at independence. Yet, despite some encouraging signs for the nationalists, countervailing electoral and economic pressures may derail independence efforts once again.

Perhaps Scottish voters might support independence

At first glance, the SNP will start the next referendum campaign under more favorable circumstances than those of 2012. Scottish independence was at that point supported by 24 percent of the population (34 percent when excluding Don’t Knows), with support rising to 45 percent in 2014 by the day of the referendum. The swing that will be required for the nationalists in the next referendum is significantly smaller, and there a number of factors that suggest propitious timing for a rerun.

The first is Brexit. The nationalists hope to capitalize upon the fact that Scotland voted 62-38 percent to stay in the European Union, portraying the outcome of the Brexit referendum as a denial of Scotland’s democratic will.

The second is the changing nature of opposition. The Labour-Conservative pro-Union coalition, “Better Together,” profoundly altered the electoral landscape in Scotland, with Labour punished by the electorate for its association with the Conservatives. Fearing further electoral retribution, the Labour Party has become far more reluctant to publicly oppose Scottish independence, which has in turn strengthened the Scottish Conservatives, who have repositioned themselves as the primary pro-Union party. The Conservatives may lose their last seat in Scotland, while the SNP is targeting Labour’s Glasgow redoubt.

The SNP will frame the next referendum as a pro-E.U. cross-party movement. It will nonetheless savor the prospect of its most visible opposition being the Conservatives, who are widely disliked in Scotland. Prime Minister Theresa May’s decision to deny the SNP a referendum before 2019 may paradoxically strengthen the SNP’s position. This position might now prove even more significant since it was justified by the desire to avoid Westminster being distracted during Brexit negotiations — a claim that now seems hypocritical in light of May’s decision to launch a campaign of her own. If the Conservatives win the national election, as is widely expected, a Conservative Westminster will look like the primary obstacle to Scotland’s self-determination. At the same time, the SNP can begin campaigning at a time when Westminster is consumed by Brexit.

But the odds are against it

However, there are two important factors that make a referendum victory less likely. The first is that most Scots disagree with the SNP’s position that a referendum should be held before 2019 when Brexit negotiations will be concluded. In fact, of those that want a second referendum at all, only 30 percent agree with the SNP’s timeline.

When do you think a second independence referendum should be held?

The SNP’s position on a second independence referendum cuts against the grain of public opinion in another, more fundamental way. Voters don’t seem to want it. Support for independence has barely shifted since the E.U. referendum result, and the majority are still against it.

Do you think that Scotland should be an independent country?

Brexit may not be enough to nudge Scottish population toward independence. Indeed, while a large majority of the Scottish population voted to remain in the E.U., a third of SNP supporters did not. This has created an uncomfortable conundrum for the nationalists. They are justifying a second independence referendum by saying that Brexit result contradicts Scotland’s democratic will, but a sizable minority of independence supporters were actually pro-Brexit. Some independence supports see the E.U. as another undemocratic union, and the pro-E.U. SNP was actually strongly opposed to Britain entering the E.U. back in 1975.

Furthermore, Scotland may have to leave the E.U. along with the rest of Britain before any vote on independence and might not be able to rejoin easily. Countries like Spain, which fear their own separatist movements, might be opposed.

Independence may be costly

The 2014 independence campaign struggled to calm fears about whether an independent Scotland would be economically viable. Those fears may be heightened in 2017.

First, global oil prices have collapsed. This is a problem for nationalists, who were planning on exploiting Scotland’s oil reserves, which at the beginning of the first campaign in 2012 were worth around £10 billion ($12.82 billion) to the Scottish economy. As of 2015-16, Scottish oil and gas revenue had fallen to just £60 million. The collapse in oil revenue has greatly damaged Scottish finances. Scotland has a deficit of 9.5 percent of GDP — twice that of Britain. At the same time, per capita spending in Scotland is £1,200 higher than the rest of Britain, a product of popular policies such as free tuition and medical prescriptions, which are important to SNP popularity.

Second, trade presents some sticky issues. The SNP argues that Brexit will hurt the Scottish economy. Scottish exit from Britain might hurt it more. Scotland does four times as much trade with Britain than all of the E.U. member states combined. Just as in 2014, the SNP has been unable to explain how independence will affect its trade with Britain and E.U., and how a hard border between Scotland and Britain would affect flows of goods, services and people.

Why is the SNP pushing for a new vote?

Without a convincing economic plan, support for independence is likely to remain low. The problem for the pro-independence campaign is that formulating such a plan is even harder now than it was in 2014. In addition, there are now a number of new factors which both exacerbate preexisting concerns while creating new ones.

If the economic, constitutional, and electoral problems are so manifold, the question then is — why now? The SNP’s problem is that legislating a referendum requires a majority in the Scottish parliament, and the trends suggest they might not have this for long. While the SNP won an outright majority in 2011, it lost it in 2016, and now relies upon the Scottish Greens to pass its legislative program. The general election will provide a useful bellwether on support for the SNP and its cause. If support continues to drop, it is possible that by the 2021 Scottish parliamentary elections — by which time the SNP will have been in government for 14 years — the SNP will not be able to push the legislation required for a referendum. In such a scenario, independence could be off the table for another generation.

Luke Mackle is a graduate student and researcher at Harvard University’s Davis Center for Russian and Eurasian Studies