PARIS — His rallies attract tens of thousands. His YouTube posts are watched by millions. In a TV debate between presidential candidates, he put his rivals to shame with quips that became internet sensations.

'Tis the season of Jean-Luc Mélenchon.

Aged 65 and making his second bid for the French presidency, the razor-tongued, Robespierre-loving, Mao jacket-wearing firebrand is shaking up the campaign.

After his TV debate success, Mélenchon's personal approval score leaped by 19 percentage points to 47 percent, prompting the right-leaning Le Figaro daily to anoint him the campaign's "superstar."

His chances in the election's first round on April 23 are also improving. Mélenchon is now expected to grab 14.5 percent of the vote on April 23 versus 1o percent for the Socialist Party's Benoît Hamon and nipping at the heels of scandal-tainted conservative François Fillon, according to Ifop's rolling daily poll.

Yet Mélenchon still stands little chance of getting elected. Emmanuel Macron and Marine Le Pen are just too far ahead. So the question remains: What exactly is Mélenchon trying to achieve? "To be elected president of the Republic, of course," the man himself deadpanned during the TV debate.

But his critics see other motivations.

None is stronger, they argue, than the prospect of punishing the Socialist Party, to which Mélenchon belonged for more than 30 years.

"There is a psychological reason why Mélenchon is doing this. He has a hatred for this party," said Gérard Grunberg, a professor at Sciences Po university who studies left-wing politics. "When he belonged to it, they did not give him enough credit ... Now he wants to kill this old Socialist Party to take its place."

'Demolition man'

If he is to do that, however, Mélenchon will have to tread carefully.

Fighting too openly with the amenable Hamon would put off many left-wing voters. So for weeks, the leader of the "France Untamed" movement was at pains to show that he was considering a deal with Hamon.

The two men held several rounds of talks. They even struck a "non-aggression pact" over a private dinner.

As it turned out, their pact was no more solid than the one between Molotov and Ribbentrop before World War II.

Beyond the odd photo opp, Mélenchon didn't move a centimeter closer to Hamon's campaign.

Now that Mélenchon's bid is gaining momentum, he is comfortable enough to publicly reject the idea of an alliance. "I will negotiate nothing with anyone at any point at this stage," he told some 5,000 supporters Wednesday evening during one of his town hall-style meetings in Le Havre.

Keeping the socialists at arm's length is one strategy. Another is to outflank them from the left, with proposals that make Hamon's program look pale and timid.

At the top of Mélenchon's agenda are abolishing France's presidential regime, the 5th Republic, via a referendum; cutting back the legal working week from 35 to 32 hours; and taxing 100 percent of any revenue that is 20 times greater than the median income.

In some ways, the differences between Hamon and Mélenchon are matters of nuance. But when it comes to the EU, NATO and Russia, there is an uncrossable bridge.

Whereas Hamon prescribes strength when dealing with Russian President Vladimir Putin, Mélenchon argues that "there is no use showing up armed to the teeth, it's better to talk with Russia."

While Hamon never suggested any fundamental realignment of France's alliances, Mélenchon wants to quit NATO and pivot France to the east, toward warmer ties with Putin and an alliance with Syria's Bashar al-Assad against Islamic State.

And while Hamon says France should revisit certain EU-mandated free trade deals, Mélenchon has a more radical plan: completely renegotiating France's relationship with the EU. If the negotiation does not bring the hoped-for results, it will be "up to the French people" to decide whether to remain in the bloc.

Le Pen-Mélenchon axis?

The other candidate that Mélenchon's foreign policy outlook chimes with is National Front leader Marine Le Pen. On the EU, NATO and Russia, there is scarcely any daylight between them.

The alignment is so great that during the TV debate, Mélenchon was unable to maintain an aggressive attitude toward the National Front leader beyond discussion on migration. Midway through the debate, they were in lockstep with both saying — almost at the same time — that the disabled should be entitled to €1,000 monthly benefits.

There are other signs of warmth. In January, Mélenchon complained that the National Front was unable to borrow money from French banks, urging them to have "pity" on Le Pen.

Conversely, National Front officials often credit Mélenchon's campaign with good tactics. Senior party operative Philippe Vardon, speaking with POLITICO earlier this year, said there were "things to retain" from Mélenchon's platform and campaign, which he called "efficient."

Gaëtan Bertrand, who runs the National Front's web operation, said Mélenchon was the only candidate besides Le Pen running a good web campaign.