WASHINGTON — The European Union is the West’s last line of defense. The United States has historically been the world’s anchor of republican ideals, but President Trump has abandoned the role, openly admiring strongmen like Vladimir Putin of Russia. As the temptations of nationalist populism spread, Europe has responsibility for holding down the Western fort. The primary battle right now is over Poland, which is deepening its descent into illiberalism. The European Union needs to take a firm stand in defense of Western values.

Since coming to power in 2015, Poland’s populist government has sought to control the news media, purged and politicized the civil service, and intimidated intellectuals and civil society organizations. Three weeks ago, Poland’s president signed into law legislation that compromises judicial independence, effectively clearing the way for the ruling Law and Justice party to stack the courts.

In response, Brussels has taken the right steps, warning Warsaw of punishment if it continues to pursue policies inconsistent with the European Union’s founding principles, which include “democracy, equality, the rule of law and respect for human rights.” In late December, the European Commission for the first time in the union’s history started a formal procedure that could lead to disciplinary sanctions, including the suspension of Poland’s voting rights in the European Union’s main decision-making body.

These measures have not gone unnoticed in Warsaw. This week, Prime Minister Mateusz Morawiecki reshuffled his cabinet, replacing a number of ministers whose relationships with European leaders were particularly strained. And he flew to Brussels for dinner with Jean-Claude Juncker, the president of the European Commission. But these moves have yet to be accompanied by any concrete steps to reverse Poland’s illiberal turn. The European Union must keep the pressure on.