With another government on the brink of collapse, is France the new Italy?

France, rather, is sliding into a morass that once plagued its southern neighbor. If French Prime Minister François Bayrou loses a Sept. 8 confidence vote on his efforts to rein in the country’s budget deficit with 44 billion euros—roughly $51 billion—in cuts, he will become the fourth head of government to lose his job in a year and a half.

High turnover in the prime minister’s office was once rare in France, a cornerstone of Europe with a political system designed to foster stable governance. In recent years, however, France has entered a vicious cycle: Deteriorating public finances are fueling political fragmentation, which in turn prevents the nation from making hard choices about how to fix its fiscal mess.

Bayrou isn’t expected to survive the confidence vote, which would leave President Emmanuel Macron having to name a new prime minister to form the next government. But last week Bayrou urged lawmakers to rally behind him as “a matter of survival for our state."

The more ungovernable France becomes, the more investors are pushing its borrowing costs to levels familiar to Europe’s debt-laden periphery. The yield on France’s 10-year bonds has risen above Greece’s and its borrowing rate is currently neck-and-neck with Italy’s.

Athens and Rome cut their budget deficits after taking painful austerity measures during the region’s debt crisis in the 2010s. Today, Giorgia Meloni is on track to become one of the longest serving prime ministers in Italy’s postwar history after nearly three years in office.

For France, pulling out of the spiral is hard because its National Assembly, the lower house of its parliament, is divided into factions, each with opposing fiscal priorities and enough votes to shift the balance of power.

The National Assembly in Paris.

An array of leftist parties doesn’t want any cuts to France’s welfare state, which accounts for 65% of public spending. Centrist lawmakers allied with Bayrou and Macron—as well as a cluster of establishment conservatives—want to boost military spending to counter Russia’s invasion of Ukraine without raising taxes. And Marine Le Pen’s far-right lawmakers say the government should cut spending by reducing immigration and payments to the EU.

Macron laid the groundwork for the current malaise when he introduced sweeping tax cuts after he was first elected in 2017 without making similar reductions to the cost of French healthcare, education and other public services. He abolished the wealth and housing taxes, lowered corporate levies and introduced a flat tax on capital gains. The combined measures meant that by 2023 the state was deprived of €62 billion in annual tax revenue, or 2.2% of GDP.

The tax cuts helped make France one of the most attractive destinations for foreign investment in Europe, and unemployment fell to 7%, its lowest level in decades. Economic growth initially picked up, helping finance tax measures, but then a series of crises hit. The violent yellow-vest protest movement ripped through the country, prompting Macron to spend €17 billion to mollify protesters.

The yellow-vest protest movement was sparked by plans to increase fuel tax.

“Macron’s policies caused a great sense of injustice and were seen as aimed at lowering taxes for the rich and for businesses," said Xavier Timbeau, an economist at OFCE, a Paris-based, state-funded economic observatory.

Measures to soften the blow of the Covid-19 pandemic cost another €41.8 billion. Then Russia invaded Ukraine, sending energy prices higher. Macron responded with €26 billion in energy subsidies.

By then, France was in a deep hole. Debt went from €2.2 trillion before Macron was elected to €3.3 trillion, and economic growth flatlined. Macron refused to raise taxes, and he struggled to trim entitlements. He managed to raise the retirement age to 64 by 2030—for an estimated €17.7 billion in savings that year—but only after a bruising battle with opposition parties and widespread protests.

Last year, France was forced into a series of embarrassing corrections to its budget deficit. The national statistics agency widened France’s 2023 deficit to 5.5% of economic output, compared with the government’s forecast of 4.9%. Weeks later, the government had to revise its forecast for its deficit in 2024, raising it to 5.1% of economic output from 4.4%. Ratings firm S&P responded by downgrading France. Conservative lawmakers threatened to help take down the government if it didn’t make more of an effort to rein in spending.

French Prime Minister François Bayrou

Macron pre-empted the parliamentary fight with one of the most consequential moves of his tenure: He dissolved parliament and called snap elections. The summer election resulted in an unprecedented splintering of votes in the National Assembly. Without a clear majority in place, any piece of legislation, including the annual budget, became a referendum on the government.

Macron’s first choice of prime minister after the election, conservative Michel Barnier, was swiftly felled in a confidence vote. Bayrou took over in late December and managed to pass an overdue 2025 budget by temporarily increasing corporate taxes.

He soon began warning parliament that even deeper sacrifices would be necessary to shrink the 2025 deficit, which is expected to reach 5.4% of GDP this year. He lost the support of the socialist party after negotiations failed to change Macron’s overhaul of the pension system.

Then, Bayrou outraged the country with a plan to boost economic output by eliminating two national holidays: Easter Monday and May 8, when France celebrates the surrender of Nazi Germany to the Allies.

Jordan Bardella, leader of the far-right National Rally, branded the idea “a direct attack on our history, our roots—against working French."

Write to Stacy Meichtry at Stacy.Meichtry@wsj.com and Noemie Bisserbe at noemie.bisserbe@wsj.com