Top EU officials are debating the state of the European Union.

EU Council President Donald Tusk said Thursday evening in Rome the idea of one European nation "was an illusion."

Nationalists and anti-European sentiment have gained ground in elections in several EU nations. Fears of being overwhelmed by migrants are testing a major EU accomplishment — Schengen "border-free" travel — as several countries erect or plan physical barriers.

Tusk acknowledged that the EU is facing a "risky and tricky" moment. But the former Polish prime minister said that while the "utopia" of an ideal Europe is "unrealistic," Europe can tackle its challenges keeping the continent's pluralism in mind.

European Commission President Jean-Claude Juncker, citing the migrant crisis, said "suddenly we discovered that not everyone was applauding or sharing" EU views.