PARIS >> Europe’s two biggest military powers took a gamble in lining up behind U.S. President Donald Trump to bombard Syria. Now they need to make sure it doesn’t backfire.

Critics swiftly accused Britain and France of playing loyal deputies to an unpredictable American leader, viewed by many in Europe with suspicion or outright scorn. Some worried it could further antagonize Europe’s hulking neighbor Russia at an already tense time.

British Prime Minister Theresa May was decried for not seeking parliamentary approval for today’s coordinated airstrikes. French President Emmanuel Macron was accused of compromising the independence of a country that famously stayed out of former U.S. President George W. Bush’s 2003 invasion of Iraq.

And worst of all, today’s “one-shot” military operation may not substantially change the course of the war in Syria.

Yet the coordinated bombings tapped into the prevailing mood among leaders of the two powers, who are united in a sense that something had to be done to stop Syrian President Bashar Assad’s government from repeatedly using chemical weapons.

“We have seen the harrowing images of men, women and children lying dead with foam in their mouths,” May told reporters. “These were innocent families who, at the time this chemical weapon was unleashed, were seeking shelter underground … This must be stopped.”

Boosters see the attack as a way to keep European voices heard in Syria’s increasingly globalized civil war. And some even hope that today’s rain of cruise missiles could push all sides closer to the negotiating table and an eventual end to the war.

For all their skepticism of Trump, many Europeans have been are brought together by an unequivocal abhorrence of the use of chemical weapons in war, since they were first used on a massive scale in World War I in Europe a century ago. The use of gas was soon outlawed, and that red line in diplomacy should not turn grey, the argument goes.

“We cannot tolerate the normalization of the use of chemical weapons,” Macron said in launching French military action, calling that “an immediate danger to the Syrian people and for our collective security.”

The move could cost both leaders domestically, however.

May said there was “no other choice” but to act fast, without taking time to recall Parliament from its break. Lawmakers are already crying foul.

While May wasn’t legally required to seek lawmakers’ approval, opposition leaders had suggested she had a moral responsibility to do so. The tainted legacy of former British Prime Minister Tony Blair’s rush to back U.S. President George W. Bush in Iraq has overshadowed the debate.

“Theresa May should have sought parliamentary approval, not trailed after Donald Trump,” said opposition Labour Party leader Jeremy Corbyn. He warned that May could face a backlash in Parliament, calling the allies’ bombing “legally questionable” and saying it risks further escalating “an already devastating conflict.”

May’s Conservative Party lost its majority last June, and since then, her government has limped from crisis to crisis.

In France, Macron is facing the worst labor unrest of his presidency so far, with strikes that halted two-thirds of French trains today and weeks more of walkouts to come.

Macron drew criticism today from the far-left to the far-right. National Front leader Marine Le Pen tweeted that the strikes expose France to “unpredictable and potentially dramatic consequences,” and criticized Macron for not taking an “independent” stance.

Yet Macron is trying to keep all his options open.

He talked to Russian President Vladimir Putin on the eve of the attacks on Russian ally Syria, and hinted that they were imminent, according to top French officials. And as soon as the strikes were over, the French foreign minister pledged to keep open channels of communication with Russia.

But in nine days, Macron goes to Washington for the first state visit under Trump’s presidency — and the French leader can’t be seen as Trump’s lapdog. He also needs to distance himself from comparisons to the 2003 Iraq invasion, which was motivated by suspicions that Saddam Hussein had weapons of mass destruction that never materialized.

Despite the political risks at home, both May and Macron seem to have calculated that not acting also carried its share of peril.

European nations want to contain what they see as an increasingly brazen Russia on its eastern borders. From the annexation of the Ukrainian peninsula of Crimea in 2014 to cyberattacks, suspected meddling in elections and the Salisbury nerve agent attack on a former spy, they see Russia as an unchecked force that can cause panic in Europe.

“It has always been Bulgaria’s position that no cause justifies the killing of innocent people, including children; that the use of chemical weapons is a war crime and the strike on Syrian targets was a response to a war crime,” said the Bulgarian government, which holds the rotating European Union presidency.

Other European leaders were more tempered. German Angela Chancellor Merkel called the military action against Syria “necessary and appropriate” — but happily let Britain and France take the lead.

Germany has taken in more than 700,000 Syrian refugees in recent years and has a strong interest in preventing an escalation that might lead to further refugee movements toward Europe. Germany is also generally averse to military action abroad.

European Council President Donald Tusk — a frequent critic of Trump — said the EU “will stand with our allies on the side of justice.”

On the streets near Macron’s presidential palace, Parisians had mixed feelings about the airstrikes against Syria.

“It’s a difficult question. It’s dangerous to face up to Russia. … but in front of a dictator who is slaughtering his population, if it’s confirmed, we cannot stay without reacting,” retiree Jean-Claude Barthez said. “So I’m putting my trust in the government of the three nations.”