Many French voters have been undecided on who to vote for president. From left: Emmanuel Macron, Jean-Luc Melenchon, Benoit Hamon, Marine Le Pen and Francois Fillon. After taking over from the deeply unpopular Nicolas Sarkozy, Hollande was meant to be a return to political "normality". But with the economy still in poor shape and then the spectre of Islamist terrorism on French soil, Hollande's popularity plunged – the lowest ever recorded for a sitting president. Many voters may simply stay at home. Political science is struggling to make any confident predictions about what this all means for the result. "I've covered French presidential elections for 30 years and I've never seen one like this one," says Philippe Marliere, professor of French politics at University College London. "This campaign has been a roller-coaster of minor, major upsets, surprises, twists and turns. And it isn't over yet."

Marine Le Pen rallies the troops in Arcis-sur-Aube. Credit:Nick Miller There's a chant I've become quite familiar with over the past week. "On va gagner." Repeat ad nauseam: "We're gonna win." It's echoing around political rallies up and down the country, sung with fervour and surprisingly justifiable optimism, by supporters of the far left, the far right, the centre-right and the radical centre. Protesting outside a Marine Le Pen rally in Arcis-sur-Aube, Claudia Sanchez holds a cardboard sign: "Yes to migrants, no to Le Pen". Her son's sign accuses Le Pen of being a "fascist thief". Credit:Nick Miller Tonight I'm hearing it in Champagne country at one of Marine Le Pen's "pocket meetings". The leader of the far-right, anti-EU Front National has made a symbolic choice of venue.

Arcis-sur-Aube, population 3000, is the birthplace of Georges Danton, whose statue stands sternly amid cherry blossom in the town square: one of the heroes of the French Revolution, one of the first to proclaim the country's rulers must make way for a new political order. French far-right presidential candidate Marine Le Pen shakes hands with Russian President Vladimir Putin in the Kremlin, Moscow, last month. Credit:AP For the Parisian ruling class, a Mélenchon vs Le Pen second round is the nightmare scenario. We're in FN heartland. The region's textile factories closed in the '80s, unemployment is high, the town is shrinking. People feel abandoned by the establishment, a local journalist explains. This year authorities from Paris foisted a bunch of refugees on the town, evictees from the infamous "Jungle" camp in Calais. The local mayor refused to take them, but it happened anyway. He grudgingly admitted they turned out to be a perfectly well-behaved group, but he was still opposed to their being here. On principle.

French hard-left presidential candidate Jean-Luc Melenchon speaks during a campaign rally in Marseille's Old Port, southern France. Credit:AP A lone few locals are protesting outside the FN rally hall. Claudia Sanchez holds a cardboard sign: "Yes to migrants, no to Le Pen". Her son's sign accuses Le Pen of being a "fascist thief", a reference to an EU expenses scandal and, of course, her politics. "We are totally against her ideas," Sanchez says. "But in the village where I live it's 60 per cent for Le Pen. It's amazing. It's always the same, they are afraid of migrants, they are afraid of losing France. I can't really understand it." Emmanuel Macron, left, greets Francois Fillon . Credit:AP A PA system plays Taylor Swift ("haters gonna hate hate hate, I'm just gonna shake it off") as hundreds of FN supporters push into the packed, un-airconditioned town hall.

A young man in jeans with a French flag drawn on his cheek tells me he is excited about the chance to change French politics. Francois Fillon and his wife Penelope. Credit:AP "France must stick with tradition," he says, when I ask about immigration. "It must stay French." There are no warm-up acts. A video punches onto screens flanking the stage. "I love France," says Le Pen in a voice-over, as she sits wistfully on a cliff, then on a beach, staring at the waves crashing towards her, probably wondering why they don't go back to where they came from. Polls have Marine Le Pen in the lead – just – making her the woman to beat for the presidency. Credit:Bloomberg

"I'm a patriot." Bass-heavy music adds a sense of danger. She wants a France that is protected and prosperous. She dreams of justice. And then she arrives in person, straight to the microphone. Her voice is hoarse, her delivery punchy. She responds to shouts from the audience with quick, witty comebacks. Attendees wave French national flags during an election campaign meeting with Marine Le Pen in Lille, France. Credit:Bloomberg For the next 50 minutes the crowd is in the palm of her hand. She starts by attacking, imitating and ridiculing her opponents. She leads the crowd in pantomime "boos" at them. "Don't forget this, they are responsible for the disaster at the moment," she says.

She expands on the "immense menace" of Islamist terrorism, imported into France through immigration, with refugees currently "disappearing into the wild" in Germany. She cites the attacks in Stockholm, London, Berlin, Brussels. "We must not get used to these dramas." The biggest cheer of the evening comes when she says the money spent on refugees would be "better used for the poor of our streets". She complains about criminality and violence, and promises more prisons. She moves on to the European Union, its technocratic "destruction of the small by the great", its expense. Seventy minutes later, she leads them in La Marseillaise and departs. The room farewells her like a rock star. Polls have Le Pen in the lead – just – making her the woman to beat for the presidency. The assumption has always been that her popularity has a natural, structural ceiling at 30 per cent – no more than a third of the country could stomach her, so the country would rally around her opponent. But since Brexit and Trump few make such predictions any more – and her opponents are not from the usual suck-it-up establishment crop.

Her vote has dipped recently: she has not had a strong campaign – hit by the EU expenses claims, and comments about France's history that cast doubt on the supposed laundering of FN of the racism and anti-Semitism it was long tainted by. But Rainbow Murray, a reader (associate professor) at Queen Mary University of London, says a lacklustre campaign did little damage. "The anti-Semitic comments offend the kind of people who would be offended anyway by other things she said. She's been consistent, and her success [in the polls] is the result of six years' hard work, not particularly related to the campaign she's had." Come April 23, her supporters will come out to vote, as they have intended to do for years. The prospect of president Le Pen terrifies the establishment – and not just in France. Australia has a freshly inked deal for $50 billion of submarines. Fairfax Media understands there are genuine concerns in the Australian military about the prospect of a submarine fleet built in a Le Pen France.

Le Pen's connections with Russia are not a matter of Trump-like speculation, they're a matter of record. Last month she met Vladimir Putin in the Kremlin and promised a new, closer relationship (he told her Russia had no intention of meddling in the election). Russian banks have propped up FN with loans in the past – and recent documents published in France allegedly exposed a plan to borrow several million euros last year from Russia's Strategy Bank, to fund this year's campaign. One well-connected political observer in Paris described the FN as a "wholly owned subsidiary of the Russian state". Australia's concerns aren't just over the submarine deal, which is now insulated from political influence. They are over the Australia-EU free trade deal, just about to enter formal negotiations, which Le Pen rejects. She is the only candidate with a specifically anti-Australia policy. The extent, or even the existence, of Russian influence in the campaign is hotly contested. But Emmanuel Macron has officially complained to authorities asking for an investigation into Russia-backed hacking of his campaign, and insiders say it is not just a political tactic – it is being taken seriously. Some even speculate that if there is a terror attack in France between now and the election – which would clearly benefit Le Pen's campaign – it should be very carefully investigated for signs of Russian influence. It's a wild theory, but even the fact it's being considered tells you the level of concern in the capital.

Many officials in the French government are privately saying they will resign if Le Pen wins, on moral principle – including senior military officers and senior diplomats. But she's not the only candidate they worry about. Far-leftist Jean-Luc Melenchon is surging in the polls – a candidate France 24 described as a "showman in a Chairman Mao jacket" and Le Figaro as "the French Chavez". After a strong TV debate performance – the only lively, witty element of an otherwise dour affair – he's come from nowhere to be even with the Republicans' Francois Fillon, and within striking distance of Le Pen and centrist Emmanuel Macron. Murray says Melenchon is funny, charismatic – and benefiting from the collapse of the Socialist candidate Benoit Hamon's vote. "The whole election is one of disappointment, it's about a rejection of candidates rather than a support for them," she says. "Anyone who wants change is disenchanted. They're stumbling from one prospect to the next without really wanting any of them. If enough of Hamon's supporters desert for Melenchon that might create a huge upset."

For the Parisian ruling class, a Melenchon vs Le Pen second round is the nightmare scenario. It's "an ex-Commie versus a fascist", one insider said. Melenchon pushes a 32-hour working week (it's only 35 now), a huge wealth tax and a retirement age of 60. France's already sluggish economy would likely be hit by a big capital flight should he win. Melenchon wants to quit NATO, the World Trade Organisation, the International Monetary Fund, the World Bank, and block European trade treaties. He's also a fan of Russia as a bulwark against US imperialism. For Australia, a Melenchon-Le Pen second-round vote would be a disaster. "Melenchon is exceptional," says Marliere. "The collapse of the Socialists has played into the hands of this guy, who has been campaigning for more than a year, constantly repeating the same things: against austerity, against [President Francois] Hollande." Melenchon did well in the previous election around the same time but it proved a short-lived peak. This time it may not. "He comes across almost as an appeasing father figure of a nation, saying things which a lot of people want to hear about how the French political establishment has let the population down," says Marliere. "He's calmed down, essentially. He appeals to a lot of people in the broad left wing in France, a lot of Green voters think he's the best. The momentum is with him."

Until recently that momentum was with Macron – the ex-Socialist banker, a walking centrist TED Talk who promised a break from politics as usual, without extreme baggage. He is still neck-and-neck with Le Pen at the front of the pack, and he would wipe the floor with her in the second round. But pundits are divided on the commitment of his supporters to get him there. His opponents have united to try to tie him to the failures of Hollande, the most unpopular president in living memory, and the mud has started to stick. "Macron is reaching the limits of the political ambiguity on which he founded his campaign: neither left nor right," says Marliere. "Where does he stand, what does he want? And in the debates he wasn't so good. "He's losing ground. It's not a major collapse yet, and I think he has enough traction to make it to the second round, but the end of his campaign is proving difficult." Murray disagrees, to an extent. "It's not that his vote has fallen apart, but just that the campaign equalised a bit," she says. "His constituency is increasingly firm for him – though an element of that is still a vote for 'none of the above', in that he is the least bad option for them. I'm not sure he has a groundswell of loyal centrists, so much as people who can't bring themselves to vote for his opponents."

Speaking of whom: Francois Fillon. The election should have been his – the candidate of the main opposition party, against a party whose president is stunningly unpopular and whose replacement candidate's campaign is a mess of contradictions. But the corruption scandal that blew up around him has not gone away: last month he was charged for misappropriating public funds, in an investigation over allegedly fraudulent payments to his wife and family. His party couldn't agree on a replacement, he remained its candidate, and now it is gritting its teeth and pushing him to the finish line. But if he is up against Le Pen in the second round, things get really interesting. Murray says a lot of the left would not be able to bring themselves to vote for him against Le Pen – because of the corruption allegations and the fact that he is pretty right-wing himself. Inside the Fillon campaign, it's another world. "On va gagner," they chant, in a hangar-like hall at Eurexpo in the industrial outskirts of Lyon. Thousands are here, brought in on coaches, the Republican core. They're a happy lot. It's a slick event. It's a very middle-class audience, and Fillon recognises it. His speech is heavy on economics, on freedom from taxes and charges, on the evils of bureaucracy.

"If the middle class suffers, all of France is sick," he says. The crowd laps up a complicated hypothetical about a middle-class person who makes a coffee in the morning and just wants to work, but can't make a good living because of Socialist regulations. He promises France will lead Europe within 10 years, taking over from Germany. He promises schools that will go back to the basics, "transfer knowledge, not dispense ideology". He promises a society that will respect authority. He promises to reduce immigration "to a strict minimum". Lyon was the capital of the Resistance. This town prides itself on fighting Nazis. Fillon draws the parallel to the totalitarianism of Islamist ideology. But there's also a subtext: the FN are kind of like Nazis, right? But after a while it occurs to me – I'm at much the same rally I was at the day before, in Arcis-sur-Aube. The rhetoric is dialled down, but the subjects are the same. This is a country of people sick of the status quo, who feel the country has gone down a dark, depressing alley. They want everything to change, so things can go back to being the same.