President Emmanuel Macron’s appointment of Michel Barnier as France’s new prime minister on Sept. 5 has put an end to two months of political deadlock and disarray triggered by the Jul. 7 parliamentary election result. But with the far right’s Marine Le Pen having emerged as kingmaker in a deeply fractured parliament, the respite for Macron, Barnier, and France could prove short-lived – and costly.

Since the founding of the Fifth Republic in 1958, France has had majority governments aligned with the president, majority governments opposed to the president (“cohabitations”), and – in the last two years – minority governments that have struggled to enact the president’s legislative agenda but have nonetheless had enough support in parliament to evade censure.

That era of broad stability is now over. Macron’s surprise election returned a hung National Assembly split into three-and-a-half ideological blocs. For the first time in 62 years, no party, bloc, or natural alliance won anywhere near the 289 out of 577 seats needed to govern comfortably or to survive censure. This means that any government that emerged was bound to be the most fragile in recent French history.

Following a brief Olympic truce, Macron finally launched negotiations to form a new government on Aug. 23. The left-wing New Popular Front insisted that it was entitled to elevate a little-known radical to the top job who’d reverse the president’s agenda and blow up France’s deficit, despite holding only one-third (193) of deputies in the assembly. Macron, who has the sole constitutional right to nominate the prime minister, refused.

Such a government, he argued correctly, would have zero chance of surviving immediate censure by Macron’s center (166 seats), the ex-Gaullist center right (47 seats), and Le Pen’s far right (142 seats). Outraged, the left took to the streets in force on Sept. 7, accusing Macron of “trampling democracy” and “staging a coup.” But it’s hard to argue with the president’s math.

And math is the main reason why Barnier was named to the post.

Yes, the 73-year-old former Brexit negotiator and veteran of the center right is a pragmatic dealmaker with an independent streak who would build a coalition of “national unity” from center right to center left. Barnier also promised to let Macron do his own thing on foreign affairs and defense, and he pledged to try to preserve the bulk of the president’s labor market and pension reforms. But he was far from Macron’s first choice. The two men had clashed in the past, and Macron exhausted several other options before finally nominating him.

Here’s the kicker, though: Unlike Macron’s first picks for the role, the former Socialist Prime Minister Bernard Cazeneuve and the center-right president of the northern French region Xavier Bertrand, Le Pen signaled that her party would not join the left in an immediate no-confidence vote against Barnier. And without her implicit blessing, no government could hope to survive contact with the National Assembly, as the left is committed to voting down candidates from the center and right.

Le Pen’s willingness to passively tolerate Barnier’s appointment suggests that, at this moment, she believes her political interests are best served by appearing to be on the side of stability rather than chaos. Moreover, she has reportedly been promised that the new government will advance her party’s policy priorities on immigration, the cost of living, and proportional representation voting – the latter a long-standing demand of the National Rally to better its chances of winning future elections.

How far will this constructive approach go? We will get a glimpse into the limits of Le Pen’s strategy when the new government is confronted with its first and toughest test in a few weeks. Facing the prospect of a destructive fiscal crisis, Barnier and his new finance minister (whoever he picks) will have to propose some way of filling a €16 billion hole in this year’s budget and introduce a deficit-cutting draft budget for 2025 by Oct. 1 to prevent punishment by the European Commission and financial markets. Both the amended 2024 budget and the draft 2025 budget will require far-right votes to pass the National Assembly.

Le Pen will then face an uncomfortable but clear choice. If she supports (or acquiesces to) draconian spending cuts, she won’t face an internal revolt, but she’ll be accused by the left and even some on the right of being a tool of the establishment. But if she precipitates the government’s collapse only weeks into her newfound kingmaker role, she’ll be blamed for plunging France into an unprecedented political and economic crisis. She will also potentially spoil her best chance to influence the country’s direction, legitimize the National Rally, and win the presidency in her fourth attempt in 2027. On balance, Le Pen will probably go the “responsible” way in this instance, choosing to edge Barnier’s government toward her preferred policies while keeping her veto powder dry for future legislative priorities.

And that is precisely the problem for Macron and Barnier. Even if they manage to steer France out of this budget crisis, Le Pen’s calculus could change at any moment – and it will be within her power to bring down the government whenever she pleases. All she has to do is add her party’s 142 assembly votes to the 193 held by the four-party left alliance – which is furious at Macron and will undoubtedly introduce, not to mention support, countless censure motions – to produce many more votes than the 289 needed for a majority.

Macron’s shock election has placed the fate of France’s fragile new government in the hands of his archrival. Quite the failure for a leader who had made it his life’s mission to consign Le Penism to the dustbin of history. Whether or not she ends up succeeding him in 2027, Le Pen has never been closer to the levers of power than she is today.