Before the war between Israel and Hamas took over virtually all of the international community’s attention, the Russian invasion of Ukraine was the most pressing crisis diplomats were seeking to solve.

In Brussels, this week had been slated as a big moment for the Europification of Ukraine, as EU member states meet for their final council summit of the year to green light both more funding for Kyiv and, finally, the opening of negotiations for Ukrainian membership of the bloc.

All of that has been thrown into question by one member state: Hungary.

Hungary’s populist PM Viktor Orban has been Western Europe’s number one problem child for some time. Even before the war in Ukraine, Hungary had form for holding the rest of the EU to ransom. Most of the big decisions made by Brussels require unanimous approval from all 27 member states. This means that every member state effectively has a veto it can use to block core EU policy, like sending billions of euros to a war-torn country or letting a country into the club.