BRUSSELS, Belgium—Nearly two years to the day after Ukraine and the European Union first initialed an agreement promising greater trade and political ties, both parties signed the pact last week in a move meant to bolster the nascent pro-Western government in Kiev. But as Russia settles into Crimea, putting an end to the post-Cold-War assumption that European borders would forever more be unalterable by force, the mood in Brussels has darkened.

The adoption of the Ukraine-European Union Association Agreement was a priority for Ukraine’s new leadership, which came to power last month after massive protests forced former President Viktor Yanukovych from office. It was his last-minute decision to scrap the Association Agreement last November that sparked the months-long demonstrations, which pressured Yanukovych into fleeing the country.

The agreement is intended to shore up the fragile Ukrainian government that replaced Yanukovych. It has been under ferocious pressure from Moscow, which annexed the Ukrainian region of Crimea and has sent agents into Donetsk and other major cities in the eastern part of the country to stir up trouble while keeping the Russian army poised for an outright invasion if or when Russian President Vladimir Putin decides the time is right.

The response of Washington and Brussels so far? Limited sanctions targeting leading figures from Putin’s inner circle as well as some pro-Russian Ukrainians. But given the enormity of Putin’s actions thus far, some worry that neither of these moves will be enough to deter further Russian aggression, never mind persuade Moscow to reverse course.

Indeed, at a summit in The Hague on Monday, U.S. President Barack Obama will have a hard time persuading the French to give up huge defense contracts with Russia, the Germans to compromise their supplies of natural gas, or the British to lose, potentially, hundreds of billions of pounds that Russians have brought to the City of London.

“These helpless and hopeless sanctions have zero influence,” said Vasyl Filipchuk, a former Ukrainian official who worked on EU integration matters. He told the Brussels Forum, a security conference sponsored by the German Marshall Fund, that Russia “violated the global order” and should face stronger punishment. Moscow should be stripped of its permanent veto-wielding seat on the Security Council, he said, and expelled from the Council of Europe, a multinational body that oversees the European Court on Human Rights. “There are plenty of other things we can do to stop this aggression,” Filipchuk. “If we don’t do it today, they will attack Donetsk.”

Kurt Volker, who served as the American Ambassador to NATO during Russia’s 2008 invasion of Georgia, said that the North Atlantic military alliance should be part of a coordinated Western response to the events in Ukraine. Ukraine is not a member of NATO, so NATO is under no obligation to defend it under Article 5 of its charter, which stipulates that an attack on one member of the alliance is an attack on all. Yet that should not stop NATO from using its resources to dissuade further Russian aggression, Volker said. “We need to think of not just imposing costs,” as sanctions are intended to do, “but being willing to rise to the challenge, in order to deter Russia from taking further steps [to destabilize Ukraine],” he said. Volker has specifically called for the deployment of NATO ground forces to member states bordering Ukraine.

That’s not likely. There appears to be very little appetite in Washington or Brussels for raising the stakes to such a degree. In an informal poll conducted Friday at the Forum, which is attended by political, business and think-tank leaders from both sides of the Atlantic, only 13.2 percent of those in attendance voted that the West should “threaten direct military intervention” if Russian troops invade eastern Ukraine. Nearly half preferred to “apply punishing economic sanctions.” The ostensible middle-ground approach, to “provide weapons an training” to the Ukrainians got about 25 perent of the vote.

Such is the cautiousness of the Europeans that only the political parts of the Association Agreement were signed Friday. The trade and economic aspects—arguably the most significant, since Ukraine is on the verge of bankruptcy—will not be ratified until after the country’s May 25thpresidential election.

The EU has long enforced stringent conditions on those nations seeking association or membership, and it was largely calls for economic and political reform that led the wildly corrupt Yanukovych regime to scrap the Association Agreement in favor of a bailout package from the far less exacting Russians instead. Indeed, Yanukovych’s ties to Moscow are wrapped up in organized crime networks. But no political parties are immune to the infection of kleptocracy in Ukraine. By waiting until May to implement the economic terms of its agreement, the EU is hoping to reassures its members that the new government in Kiev will be stable and legitimate.

Concomitantly, the EU also announced that it would speed up trade and political deals with Georgia and Moldova, two other countries seeking greater ties to Europe despite Putin’s aggressive hostility.

The tension over Crimea and Ukraine was palpable at the Brussels Forum. “We saw a clear danger of a failed state,” said Vladimir Chizhov, Russia’s Ambassador to the EU, defending his country’s intervention. This led to a confrontation between the Russian and several other attendees. “First you destabilize a country and then express concern that it’s a failed state?” Estonian President Toomas Ilves replied incredulously.

Filipchuk, the former Ukrainian government official, had even stronger words. After expressing his “respect” for Chizhov, whom he knew from his time working in Brussels, he then accused the Russian ambassador of “lying” about the situation in Crimea. It was Russia, he said, that had caused instability in Ukraine by launching a “trade war” and “blocking exports,” hardball moves that Putin undertook to try to keep Ukraine from moving closer to the West. Furthermore, according to Filipchuk, Putin has said that, “we are not an independent people.” (Asked for a response to Fililpchuk’s accusations, Chizhov told The Daily Beast, “I’ve known him for years. He used to be normal. But his views have changed.”)

The strongest rebuke to Russia came, unsurprisingly, from former Georgian President Mikhail Saakashvili, who fought a 5-day war against Russia in 2008, losing the breakaway territories of Abkhazia and South Ossetia in the process. “I have no respect for Ambassador Chizhov,” Saakashvili said, distinguishing himself from his Ukrainian colleague. “He reminds me of a character from Dr. Strangelove.” Saakashvili joined others in calling for harsher actions to be taken against the Russian government in general and Putin in particular, saying that the Russian leader “wants to act like Stalin but live like Trump.”

Asked in a Q & A session about what effect the recent crisis in Ukraine would have, Herman von Rumpoy, the head of the European Council, responded, “I fear our relationship will never be as before.” And that much seemed certain.