Read: Northern Ireland could be Brexit’s biggest casualty

So what is the backstop, and why has it galvanized Brexiteer anger? On its face, the backstop is a legal device, largely drawn up in Brussels but significantly tweaked at London’s request, to ensure that the border on the island of Ireland remains free of physical infrastructure checking the people and goods that cross back and forth each day (as it has been for two decades, and in contrast to most international borders outside the EU, such as the one between the United States and Canada).

It does so in two main ways: First, by ensuring that Northern Ireland (and not the U.K. as a whole) continues to be bound by EU regulations on food, farming, and industrial goods, so that products in these areas don’t have to be checked moving across the land border. Instead, they will be checked at the internal U.K. sea border with mainland Britain. Second, the backstop keeps the whole of the U.K. in the EU’s customs zone, meaning goods moving within the country or into Ireland are not subject to tariffs.

At its heart, however, the backstop is no mere technical fix—it poses fundamental questions of law and sovereignty, national identity and representation. The backstop is a policy proposal designed to maintain the status quo in Northern Ireland that has kept the peace for 20 years, but its critics claim that it inadvertently risks untipping that same careful balance.

Do those critics have a point? Even some key figures in May’s administration, including two senior government officials I spoke with, who asked not to be identified, admitted that there are fundamental problems with the backstop that have not been addressed. Here are five of them:

Democracy

Johnson’s attack on the backstop correctly identifies one of its most significant flaws: its patent democratic deficit.

Under the backstop’s provisions, Northern Ireland will be bound by EU law, without its ongoing democratic consent: No elected officials from Northern Ireland will be able to vote on new EU laws that will apply in Northern Ireland. It is regulation without representation. Whether this is a price worth paying for stability in Northern Ireland and an orderly Brexit is a different question than whether it is democratic, which it is not.

Where Johnson’s supporters are on far less solid ground is with the claim that the backstop is antidemocratic for the U.K. as a whole. Their argument goes that because, under the backstop, the U.K. remains in the EU’s customs territory, this amounts to staying in the EU, thereby undermining the 2016 referendum result. It does not. By definition, the U.K. will have left the EU, even if some of the EU’s laws continue to apply to part of the U.K’s territory.

Power-sharing

Irish Prime Minister Leo Varadkar and others have claimed that the backstop has public support in Northern Ireland, which therefore gives it democratic legitimacy. Varadkar cites the elections to the European Parliament in May, which saw explicitly pro-backstop parties win 57 percent of the vote.