As a relentless drizzle washed away the chalked messages of solidarity at Brussels' Place de la Bourse on Friday, two tightly bound yet antithetical responses to this week's attacks emerged in the aftermath, revealing with tense clarity the fragility of the grand project of European unity.

Both responses were expressed by the hundreds of mourners who came to lay flowers at the makeshift memorial site, as well as by those in corridors of power across Europe.

And, experts say, they will have a profound and definitive effect on the survival of the European Union.

On the one hand is the now-unanimous chorus of European countries saying they need to pull closer together, to fully share intelligence and tightly co-ordinate police bodies across the continent.

Brussels metro lineup

Lineups formed at metro stations throughout Brussels as the military checked people's bags in the days following this week's bombings. (Megan Williams/CBC)

This means, of course, putting further aside individual national sovereign interests, a move that won't come naturally.

While intelligence sharing is a very secret area, "it's now clearly in the international interest," Irish Justice Minister Frances Fitzgerald said at Thursday's emergency meeting of EU justice ministers.

"There's going to be more focus on this area and there's going to be a need for further resources in terms of border security."

It's the reference to "border security" that alludes to the other reaction in Europe: the growing insistence of many countries to take back national sovereignty. Simply put, it's a desire to control their own borders — who gets to cross them and who does not. 

Links made to migrants

The attackers killed in and arrested after the Paris and Brussels bombings are third-generation North African or "Maghreb" Europeans. Yet that's hardly stopped many here from linking the attacks to the flow of hundreds of thousands of refugees and migrants into the continent.

Within minutes of the bombs going off, far-right leaders across Europe took to social media, calling for the reinstatement of border controls within the EU and the expulsion of migrants.

Security forces

Brussels remains on high alert three days after bombings at the airport and on the subway. (Megan Williams/CBC)

Matteo Salvini, an Italian European MP and leader of the far-right Northern League party, was on his way to the Brussels airport Tuesday when the bombs exploded there.

He wasted no time in tweeting his reaction: "Wake up before we're all dead meat," he wrote, with a link to a Muslim man praying.

In another, he mocked the messages mourners had scrawled in coloured chalk at Place de la Bourse in central Brussels.

The fear of free movement within Europe was also expressed by those who came in the rain to Place de la Bourse.

Only days after the bombs that left at least 31 dead and scores injured, the square had been transformed from a place of quiet mourning to an improvised civic forum.

Small clusters of citizens stood debating the implications of the attacks.

'Look what Germany did'

"This is the end of Schengen," Rudy Glass, a thin, older Belgian man in glasses, said in reference to the EU agreement that allows for open travel within Europe. 

"We've let anyone and everyone in. Look what Germany did, look how many they've taken in. 'Yes, please! Everyone, come in! Welcome to my home!' Madame Merkel is now going to have to be very careful."

"You mustn't speak that way, monsieur," responded a distressed-looking Moroccan-Belgian man who didn't want to be named.

"You have no proof that the people coming here are terrorists. The bombers were born here. They went to school here. Do not blame immigrants."

But much of the discussion centred on what is perceived to be the epic failure of the Belgian police to foil the attacks.

Turkey said it told Brussels that it had arrested bombing suspect Ibrahim El Bakraoui last June near its Syrian border, likely as he was returning after a training session with ISIS. That warning, it said, was "ignored."

Belgium admitted it had made mistakes. Its interior and justice ministers offered their resignations, which were refused.

But already many here were fuming over the fact it took authorities months to sniff out the whereabouts of Paris bombing suspect Salah Abdeslam, who was hiding under their noses in Molenbeek.

Venting frustrations

Molenbeek is the Brussels neighbourhood well-known as the recruiting base for Belgium's disproportionately high number of foreign fighters, 500 or so as estimated by security analysts.

Madame Elliott

A Belgian woman, who identified herself only as Madame Elliott, says the Belgian government is to blame for not taking the threat of attacks seriously enough. (Megan Williams/CBC)

A Belgian woman, who identified herself only as Madame Elliot, stood with her two teenage daughters, venting her frustration.

"The government should have put far more resources into this. We pay enough taxes here in Belgium to cover the costs of a manhunt. I would have done anything to find him."

As sirens blared throughout the city on Thursday, by early evening police announced they had arrested six suspects in the same neighbourhood in which the bombers had rented an apartment and plotted the attacks.

Another suspect was arrested in Paris.

"There's no doubt [the bombings and police failure] are going to affect the European project a lot," said Pauline Massart, a security expert with the Brussels-based Friends of Europe think-tank and vice-president for operations and outreach for Women in International Security Brussels. 

Rising distrust

Massart said she is deeply concerned about the increased citizen distrust in their leaders and the leveraging of the fear by right-wing extremists against migrants and refugees.

But, she added, it was also possible this moment might provide an impetus for Europe to make some important shifts.

Pauline Massart

Pauline Massart, a security expert with the Brussels-based Friends of Europe think-tank, says she is deeply concerned about the increased citizen distrust in their leaders. (Megan Williams/CBC)

"This event has shown very clearly that the EU's foreign policy towards certain of our neighbours has been a failure through and through," she said, referring to the conflicts in the Middle East, "as has the internal policies concerning immigrant integration in Belgium."

Massart said it is time for Europe to learn from those failures, look outside its own borders for models where the integration of immigrants is successful and start investing in grassroots projects to help the process.

"This is a very loud and violent wake-up call."