A veteran firebrand of France's far left, Jean-Luc Mélenchon has a strong chance of depriving President Emmanuel Macron of controlling the next government.
He leads an alliance of far-left, left and green parties that took the president's centrist grouping right down to the wire in the first round of parliamentary elections. And he believes they can even win control of the National Assembly.
After Mr Mélenchon came a close third in the presidential election, the leader of La France Insoumise (France Unbowed) vowed to become prime minister himself to "revive the system". Now he says if his alliance, called Nupes, wins an outright majority, then Mr Macron will have to "give in" and name him as as prime minister - or resign.
That seems unlikely when voters elect 577 MPs in the second round on Sunday, but he could stop the president of winning the 289 seats he needs for a majority.
Nupes stands for Nouvelle Union Populaire Écologique et Sociale - new social and ecological people's union - and it's variously pronounced Nupe or Nu-PES.
By corralling together the combined forces of Greens, Communists and Socialists with his own France Insoumise, he attracted 25.66% of the vote, a whisker behind the centrist Ensemble alliance of President Macron.
They may have been neck and neck, but what matters is seat numbers and the pollsters suggest Nupes could win anywhere from 150 to 210 seats. Ensemble is heading for between 255 and 300 seats.
From Marxist to radical challenger
Jean-Luc Mélenchon dropped a career in teaching and journalism for left-wing politics in the 1970s. He served briefly as junior education minister under Socialist Prime Minister Lionel Jospin, but by the early 2000s, he became disillusioned with the what he saw as the Socialists' drift to the right.
He became a Euro MP as part of a new left-wing party in 2009. But it was only when he formed France Insoumise that he broke through, winning 19.6% of the vote in the 2017 presidential election.
He bettered that in the April 2022 presidential election, with 21.95% of the vote, attracting a cross-section of voters on the left and coming close to beating far-right rival Marine Le Pen to challenge Emmanuel Macron in the run-off vote.
Immediately, he announced his intention to lead the government, adopting the slogan "Mélenchon Prime Minister". President Macron has made clear it is his job to name the prime minister: "No political party can force a name on the president."
What his alliance wants
During the Macron presidency, the far-left leader has opposed his policies and backed the yellow-vest protests against economic inequality, making the most of his party's 17 MPs in the National Assembly. He has had to fend off recent criticism of his call for France to leave Nato, which not all of his new allies agree with either.
His Nupes alliance has come up with 650 policies to govern France, with an admission that they have 33 policy differences - about 5% of the programme. "The idea hasn't been to end up with an ideological fusion," he stressed.
In brief, they are calling for:
- Retirement to be lowered from 62 to 60
- The minimum wage (known as Smic) to go up by about 15% to €1,500 a month
- The return of wealth taxes on people and companies
- A freeze on the prices of basic essentials
- The creation of a million jobs.
The parties have contrasting views, for example, on the EU, which is strongly backed by the Greens and Socialists, but less so by the other two.
They have attracted the support of well-known economists including Thomas Piketty, who praises its focus on social and fiscal justice. However, pro-business think tank iFrap has warned that the programme would turn French growth negative and spark inflation, even if it did create a million jobs.
Is Macron worried?
Emmanuel Macron is unimpressed with the left-wing alliance's policies: "They quote the word taxation 20 times and the word ban 30 times, which gives you a pretty clear idea of the spirit of their programme."
He has largely steered clear of the campaign for the National Assembly, travelling to Romania and Moldova with days to go before the second round. Reports suggest he may also visit Kyiv, for the first time since Russia's invasion.
Speaking on the airport tarmac, he called on voters to provide him with a "solid majority" on Sunday in the name of "the higher national interest". That infuriated Jean-Luc Mélenchon, who denounced the scene as worthy of a "Trump-style sketch". His colleague, Green leader Julien Bayou, said the impression was of a president losing his nerve.
However, three Macron ministers will lose their jobs if they are defeated by Nupes candidates on Sunday. One of them, Amélie de Montchalin, who is minister for ecological transition, has described Mr Mélenchon's policies as being in line with the far right.
What could Mélenchon achieve?
If his alliance deprives President Macron of a majority, he has already done what he set out to do.
Without a majority, the Macron government would find it much harder to push through legislation without opposition support.
However, Nupes have set their sights on government, which would require an outright majority of their own, and that seems highly unlikely, even if they are still in the race in at least 500 seats.
Were that to happen, then Mr Macron would be forced into cohabitation with another political force, not seen since Jacques Chirac in 2002.