BELGRADE — It’s fashionable again to worry about the Balkans.

After years of relative calm, a familiar mix of political instability, territorial disputes and ethnic rivalries threatens to reignite the restive region.

And European leaders are concerned.

“If we leave them alone — Bosnia-Herzegovina, Republika Srpska, Macedonia, Albania, all those countries — we will have war again,” European Commission President Jean-Claude Juncker said he told U.S. Vice President Mike Pence last month.

Yet it’s a country not on Juncker’s list that could create the biggest headache for the EU: Serbia.

Popular resistance to the rule of Serbian Prime Minister Aleksandar Vučić, a man Brussels has stood behind for years, is growing. On April 2, Vučić won the presidency by a landslide, taking 55 percent of the vote.

But every night since, thousands of protesters, mostly young people, have come to the streets of Belgrade and other Serbian cities to demonstrate, alleging the election was rigged and accusing Vučić of trying to install a dictatorship. And so far, there's no sign the loud but peaceful protests are abating.

While there is little proof to support claims of voter fraud, the Organization for Security and Cooperation in Europe (OSCE), which monitors elections, reported concerns about campaign finance and media coverage ahead of the poll.

The group’s final report on the election isn’t expected for several weeks. But whatever the OSCE’s final assessment, the popular perception among Vučić’s critics — that he stole the election — is unlikely to change.

Speaking to POLITICO last week, Vučić, a politician not known for hiding his emotions, attributed the protests to “personal hatred” of him.

While the protestors themselves make no secret of their distaste for the president-elect, they cite a number of other factors as well — from government pressure on the media to official corruption to poor living standards.

“All of my friends are looking for a way out of Serbia,” one protester, a recent university graduate, said last week. “They see no future here.”

There have been some signs of progress. Unemployment in Serbia has fallen by about half in recent years, to 13 percent. The economy is expected to grow by about 3 percent in 2017 after several difficult years. But much faster growth is needed to lift millions of Serbs out of poverty and improve overall living standards in a country that still counts as one of Europe’s poorest.

Per capita GDP in Serbia was just $5,660 in 2015 compared to more than $35,000 average in the EU.

In private conversation, Serbs complain that many of life’s simple pleasures — be it foreign travel or a night on the town — remain out of reach.

That economic frustration has been compounded by a sense that Vučić and his Serbian Progressive party are dividing the spoils among themselves, a charge the prime minister denies.

Last year, thousands protested the secret demolition of waterfront buildings in Belgrade to make way for the construction of a multi-billion euro development funded by investors from Abu Dhabi.

The current wave of protests could reach a new high point April 25, the one-year anniversary of the demolition. Vučić’s opponents hope the nightly protests will gather enough momentum to sweep him out of office, much as the protests in the fall of 2000 forced then-president Slobodan Milošević from power.

Support among Serbs for EU accession has fallen from 67 percent in 2009 to just 43 percent today

That’s unlikely. For all the resistance to Vučić's authoritarian tactics, he continues to enjoy a strong base of support, especially in the country.

What should worry the EU, however, is that many of those protesting regard Brussels as part of the problem.

Europe sees Vučić, a former ultra nationalist firebrand-turned-modernizer, as someone with enough credibility in Serbia to keep the country on course to join the EU while also helping to stabilize the region.

Both Juncker and German Chancellor Angela Merkel have been staunch supporters of the Serbian leader.

Critics, however, accuse the EU, along with the U.S., of turning a blind eye to Vučić’s moves to thwart resistance at home to win his help in stabilizing the western Balkans.

“As stability is given priority over democracy, Balkan strongmen have become even stronger, less accountable, and more contemptuous of democratic standards,” Milan Nič, a senior fellow at Germany’s DGAP think tank wrote in a recent analysis about the region. "The result of this new paradox — with countries moving closer to the EU but further away from democracy and the rule of law — is growing dissatisfaction among citizens, accompanied by a loss of trust in the EU and further alienation from domestic politics.”

Support among Serbs for EU accession has fallen from 67 percent in 2009 to just 43 percent today, a staggering decline considering the enormous economic benefits membership would bring to the country.

So far, Europe doesn’t appear to have taken that message to heart.

In congratulating Vučić on his victory earlier this month, Juncker and Council President Donald Tusk hailed the result as an endorsement of EU aspirations.

“This vote of confidence shows that the people of Serbia fully endorse the European path you have chosen and which will lead to EU membership,” they wrote.