Mr. Geoana, the designated NATO deputy secretary general and a former foreign minister, calls the Schengen matter “a deeply political issue,” laced with prejudice. Excluding Romania “is not only unfair but illogical — the routes of migration are not across Romania,” he said. The country has successfully protected its borders, he added, having blocked much of the smuggling between the Russian and Italian mafias.

The problem goes deeper, Mr. Geoana said: “It’s associated with the Roma and Romanians in Europe. There is prejudice here, and it harms us. With three to four million Romanians working abroad, you need a scapegoat.”

Many of those workers are young, well-educated Romanians seeking a better life elsewhere in Europe. They send money home — an important contribution — but as the economy improves, officials express hope that the need for a better-trained labor force and a low unemployment rate will entice people to return.

Still, Romania has been a political mess for several years. A deadly nightclub fire in 2015 that prompted huge demonstrations brought down one government, and protests reignited in the face of institutional corruption and what many saw as efforts to undermine the judiciary, including the firing of Laura Codruta Kovesi, chief prosecutor of the National Anticorruption Directorate, in July 2018. Then came the fall of Mr. Dragnea and, later, the collapse of the coalition government. Now Ms. Kovesi is expected to become the bloc’s first chief public prosecutor, over the objections of her own government.

All this has had an inevitable impact in Brussels, even if European officials have noted the rise of younger, more liberal, pro-European politicians who did well in European elections in May. That vote saw support for the Social Democrats to fall by nearly half, and the rise of an alliance of two new parties, the Save Romania Union and Plus, which was founded by a former European commissioner, Dacian Ciolos. Presidential elections in November are expected to be closely fought.

Prime Minister Viorica Dancila has also complained about the special monitoring of corruption and judicial reform carried out by the European Commission on Romania and Bulgaria, known as the Cooperation and Verification Mechanism. Other relatively new members of the European Union, such as Croatia, are not submitted to such oversight.