We know that Prime Minister Johnson is a raucous figure with his share of enemies, some of them within his own Conservative party, if his recent no-confidence brushback in Parliament is to be believed. The indomitable Boris went so far as to admit that he has “picked up political opponents all over the place.” Now his perennial foes — the bureaucrats of the European Union — are once again readying for battle across the Channel.

The casus belli this time is the introduction Monday in Parliament by the British foreign minister, Elizabeth Truss, of a bill to alter the Northern Ireland Protocol. This fresh legislation goes beyond temporary fixes to permanent alterations. The protocol was an agreement downstream from Brexit. It was consummated between Great Britain and Northern Ireland and the European Union that governed customs and immigrations issues in a post-Brexit world.

Mr. Johnson — whom another Tory prime minister, David Cameron, once called a “greased piglet,” a compliment for his political survival skills — now will be forced to squirm between Brexit, the Good Friday Agreement, which ended the bloodshed in Ireland, and the leadership of the European Union that is threatening legal action. Better worry about borders than booze for the PM, who is at his strongest when the matters are largest.    

The bill proposed by Mrs. Truss aims to give British ministers the ability to use domestic law to override provisions of the protocol. Amongst other edits, it would create a “green check” fast lane for goods traveling from England to Northern Ireland and a “red check” process for those destined to the Republic of Ireland, which remains in the European Union common market. EU control over government subsidies would be terminated.

Of greatest moment is the bill’s provision to end the European Court of Justice’s reign as sole judicial enforcer of the protocol, a role that has long rankled those who smarted under the jurisdiction of the Luxembourg-based tribunal. The legislation would also give businesses the choice of whether to sell their goods in Northern Ireland under either EU or British regulations. The European Union “will not renegotiate the Protocol.” 

Mr. Johnson’s return to the thorny matter of the protocol has been driven by unrest in Northern Ireland. While the region as a whole voted against Brexit, the Democratic Unionists, known as the DUP, are ardent Brexiteers. They are also refusing to join Sinn Féin nationalists in the Stormont, which governs Northern Ireland, throwing the territory into disarray. For the DUP, the protocol was a betrayal in the first instance. 

The European Union, in addition to refusing to reconsider the protocol, has reacted with fury. The German foreign minister, Annalena Baerbock, tweeted “we will react as one to this breach of trust.” Mr. Johnson’s government replies by invoking the “doctrine of necessity,” arguing that failing to alter the protocol would jeopardize the Good Friday agreement by destabilizing Northern Ireland. The bloody ghosts of Belfast lurk. 

It is not only continental critics who have attacked Mr. Johnson’s plans. Sinn Féin’s leader, Mary Lou McDonald, fresh off her party’s victory in Northern Ireland, has lambasted the legislation as “undoubtedly” a breach of international law. She went on to tell Sky News that Mr. Johnson has chosen “a destructive path.” The leader of the Labor Party, Sir Keir Starmer, has promised to “scrap the legislation.”

The right course for Mr. Johnson would be to hold out for the sunlit uplands of liberty. The entire point of “getting Brexit done,” the resonant phrase that delivered Mr. Johnson 10 Downing Street, was liberation from Brussels and its strictures. It is for the “greased piglet” to slip loose of the socialist tentacles of those who would keep England bound and penned in. The way to do it is a liberty campaign to free the British economy from statism at home.