As the French prepare to vote Sunday in a presidential election marked by acrimonious debate about Russian influence in Europe, there’s little doubt about which candidate Moscow backs.

Last month, the combative populist Marine Le Pen of the right-wing National Front flew to Moscow to meet with President Vladimir Putin. It was a display of longtime mutual admiration. The frontrunner in a field of 11 candidates, Le Pen shrugs off allegations of corruption and human rights abuses against Putin, calling him a tough and effective leader. Her hard-line views on immigration, Islam and the European Union win praise from Putin and enthusiastic coverage from Russian media outlets. Her campaign has been propelled by a loan of more than $9 million from a Russian bank in 2014, according to Western officials and media reports.

Meanwhile, aides to Emmanuel Macron, the center-left former economy minister who is Le Pen’s top rival, have accused Russia of hitting his campaign with cyberattacks and fake news reports about his personal life. Although French officials say the computer disruptions were minor and there is no conclusive proof of links to the Russian state, President François Hollande and other leaders have warned about the risk of interference comparable to hacking operations that targeted the U.S. elections. The French government, aided by briefings from U.S. agencies about their experience last year, has beefed up its cyber defenses.

American politics was jolted when 17 intelligence agencies concluded in January that Russia had covertly intervened in the 2016 presidential campaign with the aim of electing Donald Trump. Such activity is nothing new in Europe, where Russia has launched a series of clandestine and open efforts to sway governments and exert influence, according to European and U.S. national security officials, diplomats, academics and other experts interviewed by ProPublica in recent weeks.

“The Russians have had an aggressive espionage presence here for a long time,” a senior French intelligence official said. “The Russians now have more spies, more clandestine operations, in France than they did in the Cold War.”

European and U.S. security officials say Russian tactics run the gamut from attempted regime change to sophisticated cyber-espionage. Russia has been linked to a coup attempt in Montenegro (the Balkan nation had dared to consider joining NATO); an old-school spy case involving purloined NATO documents and an accused Portuguese double agent; a viral fake news story about a 13-year-old girl in Germany supposedly raped by Muslims, and a caper by suspected Russian hackers who briefly seized control of an entire television network in France.

“One of the reasons Russia has been so successful has been its ability to develop tactics and techniques it selectively uses depending on the target country,” said Andrew Foxall, director of the Russia Studies Center of the Henry Jackson Society, a London think tank. “There’s a nuance to it as well. That’s something that in the West we fail to grasp.”

The French elections are the latest front in what is likely to be a conflict for years to come. Officials say France and Europe are vulnerable because of converging crises: immigration, terrorism, structural economic inequities, the Brexit vote in Britain last year, the rise of populism and extremism. The French election offers a particularly tempting target to the Kremlin, which wants to weaken and divide the West and multinational institutions such as the European Union and NATO, according to Western officials and experts.

Le Pen’s proposed policies align closely with Moscow’s geopolitical goals. She promises to reinstate national borders, abandon the euro currency and hold a referendum on whether France — which will be the EU’s remaining nuclear power after Britain’s departure — should remain in the 28-member bloc.

“For Russia, there is a desire to display power,” said Thomas Gomart, director of the French Institute of International Relations, a think tank in Paris. “They have openly chosen their candidate. It’s very serious. If Le Pen is elected, which is not impossible, that would be part of a chain of events including the Brexit and the election of Trump that would amount to a spectacular reconfiguration of the Western political family. The Russians want to weaken Europe, and to break NATO. The stakes are very high.”

Pre-election polling in France shows that no candidate has enough support to receive the required 50 percent, which means the likely result of Sunday’s vote will be a May 7 runoff pitting Le Pen against Macron or another strong challenger. Experts worry about a potential Russian spy operation, such as a Wikileaks-style disclosure of compromising information about a candidate, intended to tip the scales during that showdown.

No such direct intervention has been detected to date, and Russian officials reject allegations that they are trying to manipulate elections in France or elsewhere.

The Putin government has “no intention of interfering in electoral processes abroad,” said Dmitry Peskov, a Kremlin spokesman, in February. He complained about “a hysterical anti-Putin campaign in certain foreign countries.”

Intelligence operations — especially in the high-tech realm — are difficult to pin conclusively on a state. Moreover, Russian spy agencies have developed sophisticated capabilities in the gray areas of information warfare and political influence.

“We don’t see cyberattacks for the moment here affecting the campaign,” the senior French intelligence official said. “There are Russian influence efforts, news coverage by Russian media, the standard activity. But most of it is not illegal.”

Even some Western intelligence officials concerned about Moscow’s aggressiveness think there is a tendency to exaggerate the problem. Although European experts generally agree with the U.S. intelligence community’s conclusion that Russia interfered with the presidential race last year, those interviewed did not think it had a decisive impact on the victory of President Trump.

“Russia’s impact has been greatly underestimated, but it shouldn’t be overestimated either,” Gomart said.

As far as European spy-catchers are concerned, the Cold War is back — if it ever ended. An early sign came in 2006 with the assassination of Russian exile Alexander Litvinenko in London.

Litvinenko was an outspoken foe of Putin and a veteran of the powerful Federal Security Service (FSB), which Putin once led. In 2000, Litvinenko fled to London. He spent the next few years helping British and Spanish intelligence and law enforcement investigate ties among Russian mafias, politicos and security services.

In November 2006, Litvinenko died after three weeks of agony as the result of being poisoned with polonium-210, a rare radioactive toxin, by two Russian agents at a luxury hotel in London, according to a British court inquiry. The probe that ended last year confirmed the conclusions that Western governments and Russian dissidents reached long ago. The presiding judge, Sir Robert Owen, found that the FSB killed Litvinenko on orders from the highest levels of the Russian state, “probably” including Putin himself, according to Owen’s report.

Alexander Litvinenko, shown in the intensive care unit of University College Hospital in London in 2006, died after being poisoned with polonium-210 by two Russian agents, according to a British court inquiry. (Natasja Weitsz/Getty Images)

The 329-page report detailed the extremes to which Russian spies were capable of going in the heart of the West. The killers used a devastatingly lethal poison of a kind that is manufactured in secret Russian government labs, according to the report. The physical effect on the victim was comparable to ingesting a tiny nuclear bomb. The symbolic effect was to send a mocking message to the world about the impunity of the masterminds, since there was a good chance that the cause of death would be discovered and connected to Moscow.

Because the brutish assassins apparently did not know they’d been given polonium, they left radioactive trails across Europe during three separate missions to London, failing in their first attempt to kill Litvinenko by slipping the poison into his drink, according to the report. Although British prosecutors charged the duo with murder and sought extradition, the suspects remain free in Russia. One of them, KGB veteran Andrei Lugovoi, was elected to the Russian parliament in 2007. (Both men, and the Kremlin, deny the charges.)

The relationship between Moscow and London has never recovered, according to officials and experts in Britain and elsewhere. The scope of Russian spying in Europe has escalated steadily and dramatically, Western security officials and diplomats say. After shifting much of their energy to fighting Islamic terrorism in the early 2000s, European counterintelligence agencies have been forced to redeploy personnel and resources to confront the Russian threat.

“The spy-versus-spy activity with the Russians is very intense,” the senior French intelligence official said. “And occasionally we expel them, or give them a tap on the shoulder and tell them to cut it out. These matters are often resolved service to service, rather than through prosecuting people. The FSB still cooperates well with us on antiterrorism, even if we know their partner agencies are trying to pick our pockets and steal secrets.”

The cloak-and-dagger duel occasionally has an old-school air. Last May, a plainclothes team of Italian police detectives arrested two men meeting in a small café in the riverfront Trastevere area of Rome. The two had been under surveillance by Portuguese counterintelligence officers and other Western spy services for some time.

One suspect was Frederico Carvalho Gil, then 57, a veteran of Portugal’s spy agency. The other was identified as Sergey Nicolaevich Pozdnyakov, 48, described by European national security officials as a senior officer in the SVR, Russia’s foreign intelligence service. He had once been stationed in Italy, but was allegedly operating as an “illegal” — a spy without diplomatic cover — when he was caught. He was accused of serving as a handler for Carvalho, paying him to obtain secret intelligence related to NATO, according to Italian and Portuguese authorities.

The investigation indicated the Portuguese intelligence officer had drifted into a “double life” after a difficult divorce, according to the Corriere della Sera newspaper. Carvalho allegedly had relationships with Eastern European women and posted references on social media about his travels in Russia, according to the Corriere.

Italian police say Carvalho went to Rome to slip his handler NATO documents in exchange for 10,000 euros in cash, one of a series of such meetings in Italy and elsewhere. Still, the contents of the secret papers confiscated in Rome seemed relatively “banal” for a Russian spy to expose himself to possible capture, an Italian national security official told ProPublica.

Carvalho, who has denied the charges, awaits trial in Portugal. Italian authorities held the Russian, then sent him back to Moscow after an appeals court rejected an extradition request from Portugal.

Russian operatives take surprising risks, according to European and U.S. officials. The attempted coup in Montenegro last year is a case in point.

Montenegro, a strategically situated Balkan nation with a population of only 600,000, applied to join NATO last May. Russia lobbied strenuously against the impending membership, using diplomatic and non-governmental resources including the Orthodox Church. Russian agents stirred up protests against NATO and funded busloads of demonstrators.

Then came an uproar. Montenegro prosecutors charged that two Russian spies and two Serbian nationalists plotted last October to deploy a band of gunmen to assassinate the prime minister, storm Parliament and install an anti-NATO government. The accused spies, one of whom had previously been expelled from Poland, eluded capture. The Serbians are being prosecuted. A complex investigation continues, but Western officials say they have obtained information confirming Montenegro’s charges that Russian spies attempted the overthrow of a European government.

“The thesis is they escalated to that level because the Russian government was not happy with the way Montenegro was going,” a U.S. official said. “They were unhappy with the inability of their people operating on the ground to influence politics.”

If the Montenegro plot showed a willingness to resort to brute force, Russia-watchers say the larger strategy features more high-tech methods, such as the mix of cyberattacks and information leaks during the U.S. elections.

“Hacking is another tool in the toolbox,” the U.S. official said. “This appears to be trending toward state sponsorship and involvement. This is what worries us. The use of state power, intelligence and other methods, to affect the democratic process in European nations.”

Russia is not alone in using cyberwarfare, but it is the only nation to have combined it with conventional warfare, according to Foxall, the scholar at the London think tank. Such hybrid offensives took place during Russia’s war with Georgia in 2008 and its annexation of Crimea in 2014, he said.

Nations outside Russia’s buffer zone have not been immune, according to experts and Western officials. During the past few years, experts and officials say, suspected Russian hackers have penetrated targets including the Italian foreign ministry; the Warsaw stock exchange; a German steel mill; the European Parliament; and the computer files of a Dutch air safety team investigating a missile attack by pro-Russian fighters that downed Malaysia Airlines Flight 17 over Ukraine in 2014, killing 298 people.

“If you think of all these incidents as a whole, you reach a worrisome conclusion,” Foxall said.

The crippling hack of France TV5 Monde sent a clear message. It took place in April 2015 amid tension in Europe about the intertwined threats of Islamic terrorism and an influx of hundreds of thousands of migrants into Greece, many of them refugees fleeing Russian-backed military onslaughts in Syria.

On the day of the cyberattack, two French government ministers visited the headquarters of the network, which airs 11 channels and broadcasts in Belgium, Switzerland, Canada and other Francophone nations, to celebrate the launch of a new channel. The hackers took over the network’s programming and social media accounts, filling screens with Islamic jihadi propaganda. It took the network hours to regain control of its broadcasts and prevent its systems from being destroyed.

The hackers had breached TV5’s defenses via its email messaging networks months earlier, according to Nicolas Arpagian, a French cybersecurity expert affiliated with government think tanks. Although the hackers claimed allegiance to a “CyberCaliphate,” the investigation points at culprits linked to the Russian state, according to Arpagian and Western officials.

“The goal seems to have been destabilization,” Arpagian said. “A demonstration of capability, of the potential to disrupt.”

A policeman stands guard in front of TV5 Monde headquarters in Paris after suspected Russian hackers seized control of the television network in 2015. (Christophe Ena/AP Photo)

Definitive proof of Russian state involvement is elusive, however. Experts say the Kremlin’s 21st century approach to what the Soviets once called “active measures,” combines cyber-operations with the overt continuum of fake news, internet “trolling,” and state-controlled media.

The strategy emerged in response to the anti-Kremlin “color revolutions” of the early 2000s, when throngs of ordinary citizens took to the streets to demand the ouster of Moscow-backed leaders in Ukraine and Georgia, experts say. Russian leaders believed the United States was using “soft power” means, such as the media and diplomacy, to cause trouble in Russia’s domain. The Russians decided to develop a comparable capacity. But the result wasn’t soft very long, especially as the Kremlin became concerned that events such as the Arab Spring could spark unrest in Russia, experts say.

“The logic of influence and projection overseas was replaced by the concept of ‘confrontation with the West’ and the image of a ‘besieged fortress,’” wrote Céline Marangé of France’s Institute for Strategic Research at the Military Academy, in a study this year. “Without completely disappearing, the notion of soft power has been eclipsed by that of “information war,” whose acceptance is literal and extensive in Russia. In Russian defense and security circles … and in numerous prime-time television debates, there is an almost unanimous thesis: a worldwide ‘information war’ at the global level pits Russia, like the Soviet Union in its day, against the West.”

The combatants range from teams of “trolls” in warehouses who bombard selected targets on social media to provincial journalists who concoct wild tales following general directives rather than explicit orders, according to experts and intelligence officials. Putin’s government is presented as the lone guardian of traditional Christian values fighting barbaric Muslim hordes and a soft, decadent West. The relentless narrative: Europe is under assault by crime, Muslims, terrorism, immigration, homosexuality, political correctness and effete bureaucrats.

Occasionally, fake news stories go viral and flood into the venues such as the Russian-backed RT television network and the Sputnik news agency, whose slick content reaches an increasing audience in Europe and the United States.

One example: the horrifying tale of “Lisa,” a Russian-German teenager who told police she was kidnapped and raped by three men resembling Muslim immigrants. The case erupted in January of last year. Europe was on edge because of the very real and ugly spate of sexual assaults on women by groups of men, many of them of Muslim descent, during New Year’s Eve celebrations in Cologne, Germany.

The German authorities insisted from the beginning that there was no proof of the girl’s allegations. But the Lisa story gained momentum, driven by heavy, sometimes inaccurate coverage on Kremlin-backed and pro-Russian outlets as well as social media. The frenzy reached the point that Russia’s foreign minister, Sergey Lavrov, said at a news conference that German authorities appeared to be hushing up the incident out of political correctness, according to news reports.

Soon, however, the teenager admitted to lying. She had stayed overnight at the home of a 19-year-old male friend without permission and invented the rape story to explain her disappearance, according to media reports.

There is no evidence Russian operatives played a role in creating the initial story. But the German government and other critics have rebuked the Kremlin and the Russian media, saying they amplified and distorted the case even after it was shown to be untrue.

“The story was totally fake,” Foxall said. “This is a well-established pattern. Other stories have travelled such a path, but without the same kind of success.”

Nonetheless, Russian influence campaigns find a more welcoming political atmosphere in Europe than in the United States. After all, leftist parties in France, Italy and other nations had strong ideological and financial ties to the Soviet Union during the Cold War. There is also a pro-Russian tradition, often fomented by anti-Americanism, among some rightist and nationalist parties.

Russia spends considerable money and energy wooing sympathetic European politicians and activists. They are often, though not always, populist, nationalist, fascist, far-left, anti-system or just plain disruptive. The most powerful unabashedly pro-Moscow figure is probably Le Pen, whose presidential campaign has thrived partly because of her effort to distance herself from the angry, anti-Semitic image of her father, National Front founder Jean-Marie Le Pen.

The list also includes Nigel Farage, the brash British politician who oversaw the underdog campaign for the Brexit, and admires both President Putin and President Trump; Nick Griffin of the far-right British National Party, who after observing Russian legislative elections in 2011 pronounced them “much fairer than Britain’s”; and Matteo Salvini of the rightist and separatist Lega Nord (Northern League), which along with the populist 5 Stelle party constitutes a large pro-Moscow bloc in Italy.

To be sure, more moderate leaders in Europe also favor stronger ties to Russia and have good relationships with President Putin. Among them is former French Prime Minister François Fillon, the center-right presidential candidate competing for a spot in the runoff election.

Russian officials and their European allies argue that Moscow’s legitimate diplomatic outreach is being demonized. But European government officials worry about activity that crosses the line into funding, recruitment and manipulation by spy agencies.

“I think some of our political parties are vulnerable to infiltration,” the Italian national security official said. “They don’t have the experience, the anti-bodies, to fend off such formidable intelligence services.”

And there are concerns about wider repercussions. In January, the Center for International Research at Sciences Po, one of France’s most prestigious universities, abruptly canceled a scheduled appearance in Paris by David Satter, an American author. Satter is a well-regarded foreign correspondent who has spent four decades covering Russia. In 2013, he became the first U.S. journalist expelled from the country by the Kremlin since the Cold War. His latest book, “The Less You Know, The Better You Sleep,” details allegations that Russian intelligence services were covertly involved in mass-casualty terrorist attacks in Russia.

The cancellation caused a fierce debate about censorship when a leaked email revealed that administrators made the decision because they feared reprisals against Sciences Po students and researchers in Russia, citing the “current context of tensions,” according to Le Monde newspaper.

Despite the tensions in Europe and the concerns about interference, recent elections in the Netherlands went off without problems, with the party Moscow favored running well behind. The next test will be Sunday’s vote in France, where cybersecurity agencies are on alert. The government has taken precautions such as requiring the estimated 1.8 million French voters living overseas to cast their ballots by mail or proxy, rather than online, according to French officials.

“What we have seen so far is enough to conclude that the Russians have carried out an influence campaign,” a French diplomat said. “But I don’t think it will have a significant impact on the outcome of the election. We have to stay calm.”