Benoît de Saint Sernin is a leader of La Manif Pour Tous (Protest for Everyone), which has opposed the legalization of same-sex marriage in France. (Matthieu Alexandre/For The Washington Post)

Steeped in conservative rage and tasting of grass roots, a political backlash has traditional politicians and the news media asking the once-unthinkable: Is le tea party brewing in France?

If it were, it would be populated by the likes of Catherine Mas-Mezeran, a Parisian mother of three who wrinkles her nose at the mention of President François Hollande. She calls him “the Socialist,” which, technically, he is. But if President Obama had the birthers, Hollande now has the baptismists.

Like others in a growing movement here, she firmly believes an unsubstantiated rumor emanating from conservative circles that Hollande may have secretly renounced his Christianity. “He has rejected his baptism,” she said. “This is really shocking.”

An Elysee Palace spokesman responded, “This rumor is as ridiculous as it is unfounded.”

The movement’s strength in numbers, however, cannot be ignored. Initially a reaction to a same-sex marriage law passed last year, the movement has morphed into the most sustained mobilization of social conservatives here in more than a generation.

French President Francois Hollande has made Interior Minister Manuel Valls his new prime minister, replacing Jean-Marc Ayrault, who, with other ministers, took the blame for the Socialists' defeat in local elections. (Reuters)

A reinvigorated right delivered a devastating blow to Hollande in Sunday’s local elections across the country, prompting a humbled Hollande to reshuffle the French government on Monday. He replaced Prime Minister Jean-Marc Ayrault with Interior Minister Manuel Valls, a politician considered more palatable by some on the right.

Results of the runoff vote showed the far-right National Front scoring its biggest victory ever, taking 11 towns and a major district in Marseille in part by appealing to outraged residents. The left ceded more than 150 other cities to the center-right Union for a Popular Movement (UMP).

Losses by the Socialists also reflected economic doubts and disenchantment with Hollande. But across Europe — a continent often viewed on the other side of the Atlantic as a bastion of liberal thought — several nations are in the throes of their own full-blown culture wars, and perhaps nowhere are they raging quite as fiercely as in France.

Tens of thousands of people are taking to the streets in repeated protests, many for the first time in their lives. They are organizing assemblies and social-media campaigns even as some angry newcomers run against incumbents on the right whom they consider not socially conservative enough.

A show of strength on French streets in February led Hollande to backtrack on a measure that opponents feared could have helped same-sex couples have children through in vitro fertilization and surrogacy.

Scores of social conservatives took their children out of public schools for one day in January to protest new lessons being tested in some French schools aimed at dispelling gender stereotypes. The social conservatives said the lessons could lead to boys wearing dresses and girls playing mechanic, or even masturbation classes for children.

“We are witnessing the rise of a tea party of the French,” Valls warned in the newspaper Journal du Dimanche.

A continent already hit by economic upheaval is confronting a wave of bitter societal polarization over a host of issues such as euthanasia, abortion and same-sex marriage.

In Spain, the conservative government of Prime Minister Mariano Rajoy is seeking to push through legislation that would greatly limit abortion rights, unleashing a bitter confrontation with the left and reversing the steady march of liberal social policies there since the death of Gen. Francisco Franco. In Poland, a measure that would grant same-sex civil partnerships failed last year because of major opposition, prompting Prime Minister Donald Tusk to say he saw no chances of such unions passing within the next 10 to 15 years.

During Germany’s national election campaign last year,

center-right Chancellor Angela Merkel sparked outrage among progressives after expressing doubts about full adoption rights for same-sex couples. “To be completely honest with you, I’m having difficulty with full equality,” she told public TV.

Although dubbed the “tea party, à la Française” by some, the mobilizations here are in many respects still oceans apart from the conservative crusade that upended American politics following Obama’s election. There also is no primary system in France to give social conservatives a decisive political voice. In addition, the conservative revolution here is far more social than fiscal. While some are indeed railing against high taxes and public waste, big government is still generally considered good government in France, no matter your spot on the political spectrum.

The largest organization in the social conservative movement here — La Manif Pour Tous, or Demonstrations for All — formed in direct response to Hollande’s same-sex marriage law. But it has splintered because of infighting, even as the number of other politically active conservative groups has grown. Today, the broader movement remains a loose network of disparate interests.

And this is, well, France, a nation of cultural cues, even for social conservatives, that would perhaps not go over so well at a tea party convention. For instance, one radical splinter group of French male conservatives — the Hommen movement — is protesting gay rights by writing slogans on their bare chests while donning pants in shades of red, yellow and lavender.

Yet, observers say, comparisons to the U.S. tea party movement are not entirely off. The movement is politicizing a new class of conservatives — many of them religious — who were previously under the radar, leading to challenges for politicians on the right who have veered too close to the center. The movement also is beginning to gain a perch in the center-right UMP of former president Nicolas Sarkozy, with social conservatives forming Common Sense, a new movement within the party that is pushing “traditional family values.”

And although the movement remains fragmented and lacks a fresh-faced leader to rally around, all adherents share one thing in common: a visceral loathing of Hollande.

Given the portrayal of the tea party here as a group of political extremists and loons, many French social conservatives are bristling at the comparisons. But others say they see some similarities. “In a way, yes, on values, I think we could be described as a kind of tea party,” said Madeleine de Jessey, 24, a co-founder of the Common Sense movement within the UMP. “But economically speaking, we are not conservative like them.”

The convergence of social conservatives has made for strange bedfellows, even for France.

Upper-middle-class Catholics are on the march, but so are conservative Muslims, some of whom voted for Hollande. Some analysts here compare the current shift in France to the Reagan Democrats, when American working-class voters moved to the right. Add the stagnant economy and stubbornly high unemployment rate under Hollande, and it could be a recipe for political disaster.

On the second floor of a cafe by the Seine, within sight of the Louvre, Mourad Salah, 48, was listening raptly to a recent meeting of social conservatives involved in the new take-your-child-out-of-school-for-a-day protest. Organizers groused about liberal policies taking root in French schools, saying that a boy had been “forced” to dress up as a princess for a school party, and that books circulating among children now include one called “Daddy Wears a Dress.”

“I voted for Hollande, but never again will I vote Socialist,” said Salah, a factory worker who kept his four children home from elementary school for that day in January to protest new lessons. “They are backing policies that are affecting our children. I now understand that they have betrayed us.”

Some analysts say the nature of the French political system makes it unlikely that the movement will gain significant influence within major parities. But in a country where even the far-right nationalists have endorsed same-sex unions, if not marriage, others say it represents the start of an effort to push conservatives further to the right again on social policy.

In Versailles, a conservative stronghold just outside Paris and the former home of French kings, Benoît de Saint Sernin, for instance, had thrown his hat in for the mayor’s race when the French went to the polls for local elections. The 44-year-old political newcomer and owner of an industrial espionage school ran against an incumbent from the UMP. A strident supporter of Manif Pour Tous who opposes same-sex marriage and adoption by gay couples, he lost his bid but said his candidacy had forced his opponent to reposition himself as a more strident social conservative. The broad success of the National Front on Sunday, meanwhile, suggested that arch-conservatives may be on track to make record gains in elections for the European Parliament in May.

“The left and right in France have become the same thing,” he said. “And traditional politicians will suffer.”

Virgile Demoustier contributed to this report.