If President Macron once held youthful vim and vigor as a trump card of sorts,  that card now appears to be in the hand of Jordan Bardella — the right-hand man of Mr. Macron’s chief political nemesis, Marine Le Pen.  Not yet 30, Mr. Bardella is since 2022 president of France’s largest parliamentary opposition party, the National Rally.

Ms. Le Pen, who headed the party before that, now leads the RN in parliament, with Mr. Bardella doing double duty as a member of the European Parliament. Both Ms. Le Pen and Mr. Bardella now see it as their duty to overturn certain EU treaties and lead the charge against unchecked “Vonderleyism” — a reference to the polarizing president of the European Commission, Ursula von der Leyen.

What is transpiring in the upper echelons of French politics may not spell immediate defeat for Mr. Macron, but it might have him reaching for l’aspirine. At Paris on Thursday, Ms. Le Pen and Mr. Bardella, who is at the head of the National Rally’s list for European elections in June, told French journalists that he means business.

Mr. Bardella said he is giving himself “100 days to win” those elections, which in his view “will be unlike any other.” That is because they are shaping up to be as national for EU member countries as they will be European as a whole. For France, that means an opportunity to prepare for the presidential elections in 2027, at the end of which, if the National Rally wins, Mr. Bardella will propose “rewriting the European treaties.”

Mr. Macron, already trailing Ms. Le Pen in popularity ratings, is facing strong headwinds going into the European elections. For one thing, his Renaissance party, also trailing the National Rally in polling, has yet to even find an EU candidate. Moreover, the former socialist has been unable to capitalize on growing public discontent with many EU policies that leave in the lurch French independent action on a host of issues, from agricultural policies and the Green Deal to immigration. 

Little wonder that Mr. Bardella lashed out at both Mr. Macron and Ms. Von der Leyen, saying he would fight “Vonderleyenism” and proponents of a liberal Europe who in his view will lead the Continent to “suicide.” Mr. Bardella accused Ms. von der Leyen of wanting to turn the EU into a “railway station” — and he suggested treating the elections as a “referendum” on migration.

At the same, Marine Le Pen has tried to distance the National Rally from Germany’s rising AfD party, which ignited a firestorm recently over some of its members’ support for the idea of “remigration.” In the run-up to June, Ms. Le Pen will try to nudge her party more to the center as the jockeying for political alliances heats up. 

Mr. Bardella again took aim at Europe’s so-called Green Deal, calling it a “punitive ecology turned into a system.” Earlier this year a half-dozen members of the National Rally’s European parliamentary delegation signed a resolution to scrap it. As one of the more prominent Eurosceptic parties, the National Rally is opposed to enlargement of the bloc.

Mr. Bardella doubled down on that by asking, “When a structure doesn’t work with 27 members, why would you want 36?” On foreign policy the National Rally could be on less firm ground than Mr. Macron. Mr. Bardella called the French president’s recent remarks about not ruling out the possibility of sending troops to Ukraine “deeply irresponsible.”

Mr. Bardella also said the remarks could “weaken the French position, playing into the hands of the Kremlin.” He assailed those like Mario Draghi who want a “centralized, unitary European state, going beyond federalism.” He defended nationalist parties like the National Rally as favoring a “Europe of Nations.”

In a pointed reference to Brexit, Mr. Bardella said that if the “Europe of Nations” does  not want to utter the word “Frexit,” that is only because “you don’t leave the table when you’re winning the game.” His new “tricolor” strategy — a nod to the three colors of the flag of the French Republic — aims to “redefine the foundations of the European alliance of nations” by “changing everything without destroying anything.”

That would ultimately mean “rewriting the treaties” that stitch the EU together. Those aspirations could only materialize with a win for a National Rally candidate — Ms. Le Pen, presumably — in presidential elections in 2027. Little wonder then that Mr. Bardella likened the upcoming EU vote to a midterm election. 

His evocation of “laying the foundations for a new negotiation” with the European Commission and imposing French “red lines” could portend a long season of thorny relations between Paris and Brussels. 

As of now, nationalist parties are leading the polls for the European elections in a dozen EU countries, including France, Italy, and Austria. That not only puts pressure on Mr. Macron, but exposes the increasingly weak hold the left has, if any, on European voters.