Even before the smoke clears at the Brussels airport and over the EU quarter, this much is certain: the second major terror attack on Europe in just four months will upend the politics of everything from refugee policy to security to Brexit.

Like the assaults that struck Bohemian Paris in November, leaving 130 dead, Tuesday's coordinated attacks were intended to remind Europeans of their vulnerability.

On that score, the terrorists succeeded.

As medics carted blood-soaked corpses from the bowels of the Brussels metro, EU officials were holed up in their glass-fronted offices overlooking the sidewalk, watching in disbelief.

“So many times I passed by these locations. Why do they hate us so much?” asked Franziska Brantner, a German Green MP and former member of the European Parliament, on Twitter.

The attacks, as one commentator on the scene put it, “hit the middle of Brussels’ heart.”

And Europe’s too.

"This terror assault was not only directed at Belgium but at our freedom, our freedom of movement, our mobility and everyone who is part of the EU,” German Interior Minister Thomas de Maizière said in Berlin.

That the assaults occurred within days of the arrest of Europe’s most wanted terror suspect in Brussels, in what authorities at the time described as a major blow to the terrorists, will only increase a growing sense of helplessness.

The question now is whether the EU’s 28 members respond to the threat — after the initial expressions of shock and promises of solidarity — as allies with a common sense of purpose or by retreating along national lines.

The answer will go a long way toward determining the Union’s future or if it even has one.

There’s no good time for a terrorist attack, but Tuesday’s assaults could hardly have come at a less opportune moment for the EU.

Even as the bloc navigates the refugee crisis, it’s also trying to prevent its network of open borders from collapsing and keep the U.K., its second largest member, from breaking away altogether.

At the same time, wide swaths of the EU are struggling with high unemployment and prolonged economic stagnation, further denting public confidence in Europe’s institutions.

Rise of the populists

If the recent past is a guide, Europeans will have difficulty moving beyond the politics of fear that has permeated the bloc’s recent debates. France, for example, reacted to the November attacks by re-imposing border controls and making it clear that it has very little appetite to accept Syrian refugees. While that reaction is understandable, it’s not conducive toward finding common EU solutions.

Like Paris, the Brussels attacks present a feeding frenzy for secessionists and the resurgent anti-immigrant populists.

They wasted little time in seizing the opportunity.

“This horrific act of terrorism shows that Schengen free movement and lax border controls are a threat to our security,” said U.K. Independence Party Defense spokesman Mike Hookem, an MEP.

He cited Interpol’s estimate of 5,000 jihadists who have entered the EU from Syria, noting that 94 of them are believed to be living in Brussels’ infamous Molenbeek neighborhood.

“Brussels, de facto capital of the EU, is also the jihadist capital of Europe. And the Remainers dare to say we’re safer in the EU,” tweeted Telegraph columnist Allison Pearson Tuesday morning, before the blood had even been mopped off the floor.

In another indication that the attacks could boost the Brexit camp, the pound sank against the euro.

Another job for Merkel

Challenging that narrative, which will undoubtedly seep into national debates across the EU, will require convincing leadership and resolve. As on so many other fronts in Europe these days, only one leader possesses the requisite political skill and stature for that role — Angela Merkel.

In Brussels on Friday, Merkel predicted that the EU’s latest refugee pact with Turkey would face many serious challenges. It’s unlikely a major terrorist attack directed at the EU was part of her calculus.

Her first challenge will be to convince the rest of Europe to honor the controversial deal to extend Turkish citizens visa-free travel and take in more Syrian refugees.

As part of the agreement, Europe pledged to accept a larger portion of the 2.7 million Syrian refugees now stranded in Turkey once Ankara has shown that it can secure its coastal border and prevent people from fleeing across the Aegean.

But the terror attacks could spook Europe into closing its doors even tighter. Whether the attackers turn out to be refugees or not is beside the point. Across Europe, the big fear is one of Islamization.

That’s even the case in Germany, where concerns over the long-term impact of accepting more than one million Muslim refugees last year is fueling a backlash against Merkel’s policies.

“It’s enough!” tweeted Marcus Pretzell, a regional leader with the right-wing Alternative for Germany, a party that opposes accepting more refugees.

Even if Merkel succeeds in keeping the EU’s refugee strategy on course, the Schengen treaty may be on its last legs.

Many view the open border pact that allows for passport-free travel across most of the Continent as the essence of EU membership.

Yet it is difficult to defend in the face of terror. A number of countries, including Germany, have already reintroduced perfunctory checks at many borders.

Earlier this month, European leaders presented a plan to restore open borders by the end of the year.

The Brussels attacks will likely dash that hope. Just as Schengen allows for the free movement of goods and people, it also allows terrorists move seamlessly from one jurisdiction to another.

In the wake of Brussels, it will be difficult for even the most liberal European politician to oppose calls for stricter controls.