From the rubble of two world wars, European countries came together to launch what would become the world’s largest experiment in unification and cooperative: shared sovereignty. But, despite its impressive achievements over the decades, the European project now risks disintegration.

An unresolved financial crisis, a refugee crisis, a deteriorating security environment and a stalled integration process have created throughout Europe a toxic, unstable political environment in which populism and nationalism thrive. Perhaps the clearest manifestation of this is the erosion of the rule of law in the European Union.

Two EU members in particular, Hungary and Poland, are now jeopardizing hard-won European democratic norms — and thus undermining the very purpose of European integration.

In Hungary, liberal-democratic values have come under systematic attack from Prime Minister Viktor Orban’s government. Since his return to the premiership in 2010, Orban has committed Hungary to an authoritarian nationalist path, and he has exploited the refugee crisis to cement a “siege mentality” that helps him sustain popular support.

In the process, fundamental rights have been ignored, media freedom has been curbed, refugees have been demonized, and Orban is doing everything in his power to weaken the EU. Attempts by EU institutions to convince Orban to change course have only emboldened him to commit further outrages against democratic norms.

Meanwhile, a democratic crisis has emerged in Poland as well, starting last October, when the Law and Justice (PiS), a Euroskeptic party that also opposes immigration, secured an outright parliamentary majority by promising to implement populist economic policies and “put Poland first.” Yet, since the election, PiS has launched a series of attacks on the Polish constitution itself.

Government legislation aimed at reforming Poland’s Constitutional Court has been condemned by the Court itself and the European democracy watchdog, the Venice Commission. The government has effectively precluded the Court from ruling on the constitutionality of legislation. This weakens a key pillar of the democratic rule of law — and thus is highly problematic for Poland and Europe alike.

Hungary and Poland are the leading edge of a far-right agenda that has taken hold throughout Europe, pursued by parties that are exploiting the political vacuum created by the EU’s failure to address the financial and refugee crises. So how can the tables be turned?

In democratic countries, it is vital that democracy’s enemies be fought with democratic means. It is vital that the outside world impress on the Hungarian and Polish people themselves that in a globalized world, nationalism offers only false security and economic irrelevance. Both countries, at the heart of Europe, have profited enormously in every sense from EU membership; they must not throw away their opportunity to make further progress.

Hungarians and Poles rejected international isolation in 1989. After the fall of the Iron Curtain, both countries became staunch NATO allies even before they joined the EU. The geopolitical and security arguments for European unity are overwhelming, and there can be no united Europe without Hungary and Poland.

But all of us, and in particular the peoples of Hungary and Poland, must remember that NATO, like the EU, was founded on the fundamental principles of democracy, individual liberty and the rule of law. A government that flouts those principles jeopardizes the coherence and solidarity of the alliance.

It is therefore vital that the United States and other NATO allies speak out now and insist that functioning democratic checks and balances are safeguarded. It would be unimaginable for NATO heads of state to go ahead with their planned leadership summit in Warsaw in June if Poland remains in its constitutional crisis, with the government disregarding the rule of law and the opinion of a respected international body.

Hungarians and Poles must be reminded that Russian President Vladimir Putin is actively attempting to divide and weaken the EU and NATO. If Europe is to face down aggression from the Kremlin, it is essential that Poland and Hungary adhere to these groups’ fundamental values and principles.

But it is also necessary that the EU itself develop a more comprehensive mechanism for safeguarding the rule of law within the Union. The EU has mechanisms to regulate economic policies, safeguard the environment, and police the single market. But Europe has always been much more than an economic project; it is also a union of values, which no member can be allowed to repudiate without consequence.

Governments are created and fall apart, and politicians come and go; but democratic institutions should be spared from political interference. The sad reality is that, were they to apply for EU membership today, neither Hungary nor Poland would be admitted. Their people should weigh carefully what that means. Their current leaders claim to be defending national interests. But is it really in their countries’ interest to be sidelined by the U.S., NATO and the rest of Europe?

By Guy Verhofstadt

Guy Verhofstadt, a former Belgian prime minister, is President of the Alliance of Liberals and Democrats for Europe Group in the European Parliament. — Ed.