From abortion to the appointment of judges, the number of topics that the current Polish government and Brussels are agreeing on is dwindling. Tensions are, unsurprisingly, rising. The Polish Constitutional Tribunal’s K 3/21 decision earlier this month yanked up the emotional pressure. Why? The Polish Court essentially deemed three articles (1, 2 and 19 - all referring to the European Court of Justice) to be unconstitutional, thereby rejecting the principle of the primacy of EU law. Precedential history The primacy of EU law is he notion that EU law takes precedence over that of member states. Although it is now seen as a major organ of the nature of the Union, it was not explicitly enshrined in 1957's founding treaty. Only seven years after this did the ECJ rule that its treaties had created a new legal system in which national courts were bound to respect EU law. The Court ruled that law could not vary between member states, without making the attendant obligations contingent. Member-state courts were initially sceptical, but over time it became an accepted and integral component of the bloc’s effective functioning. Without it, if each national court or parliament had a downstream veto on the EU’s intricate lawmaking process, the EU would become essentially an empty shell according to academic Nicole Scicluna. "The EU would simply not exist" without legal primacy, is how Professor Paul Craig put it. The fightback As such, the EU-wide backlash to the Polish Constitutional Tribunal’s was wholly predictable. Poland’s government has been facing increasingly heavy criticism for its “democratic backsliding”, most notably over a disciplinary chamber it established to oust judges that were (incidentally) hostile to the government’s agenda.  On 7 October when the Polish ruling was announced, the European Commission punched back: President Ursula von der Leyen pledged to use “all the powers” at her disposal to protect the implementation of EU laws. The Commission has since frozen €36 billion in Covid recovery funds meant for Poland over its rule of law concerns; the ECJ has also ordered the Polish government to pay €1 million per day in fines after it refused to suspend its controversial disciplinary chamber. Not the usual culprits  In the midst of this ruckus, a prominent European politician stressed that “we must regain our legal sovereignty, and not be permanently cowed by a ruling or a condemnation from the ECJ”. This criticism did not come from the Polish Prime Minister Morawiecki, nor did it come from his Hungarian counterpart, Viktor Orban. Surprisingly, the speaker was a certain Michel Barnier. Barnier’s statements can be read in two ways. When asked by pan-European media, Barnier stuck to the EU line - condemning the Polish K 3/21 decision by arguing that “in Poland it is not a question of law, it is a political question, the current government is trying to coerce the judiciary”. Yet when commenting on the same news to a French audience, Barnier - in his outfit as a French presidential candidate - took the opposite view.  That the EU’s former chief Brexit negotiator, seen by many as a standard-bearer for the EU and its values, would sour on the primacy of EU law (albeit for electoral reasons) points to a malaise that has grown countries beyond Poland. Barnier’s comments express an anxiety that EU law has excessively constrained the national levers of policy, especially on matters of immigration. Off the record, many French diplomats have expressed their discomfort with European judges, who they perceive as acting like zealous missionaries rather than “the mouth of the law”, Montesquieu’s view of their role in The Spirit of the Laws. Trending where? Piling on to this political battlefront, a string of national rulings has underlined an increasingly haphazard relationship between EU law and the courts of member states. As recently as last year, the German Constitutional Court ruled against the European Central Bank’s public sector purchase programme on secondary markets. A few weeks ago, the French Constitutional Council fleshed out the possibility of a “constitutional review” of some provisions of EU law should they pose a “threat to France’s constitutional identity.” The Polish Tribunal, however, went straight for the jugular, attacking the treaties themselves rather than specific Commission-led directives. Nonetheless, Poland has illustrated a real grey area on the articulation of EU law and national constitutions, one that remains a minefield even for the legal experts.  When European citizens, who had never formally voted on the primacy of EU law, were finally given a chance to enshrine the concept in a 2005 referendum, they turned it down. Even the 2008 Treaty of Lisbon did not include the primacy of EU law. Whilst fears of a “Poleave” or “Polexit” remain largely overblown—Article 50 must be triggered voluntarily—the EU is entering terra incognita if Polish courts double down and refuse to guarantee th...