Unlike in the United States, candidates in France's presidential election have actually made the national debt a central campaign issue, as a new president is due to take charge of the eurozone's second-largest economy next year.

A French presidential debate last month was dominated by the country's rising public debt. By contrast, midterm election races in the U.S. revolve around data centers, higher gas prices, and the Iran war, even as America's own mountain of debt reaches $40 trillion.

While U.S. lawmakers largely ignore the issue, financial markets do not. Treasury yields have jumped in recent weeks, along with those of other heavily indebted countries such as France.

France's public debt now tops 116% of GDP, a worse ratio than the roughly 100% for the U.S. when measured by publicly held debt. France's economy, meanwhile, has been mired in low growth in recent years, while the AI boom has been turbocharging American GDP.

Far-left presidential candidate Jean-Luc Melenchon is campaigning on a plan to have the central bank simply cancel its holdings of French debt. With a lighter debt burden, the French government could then spend more on social programs, in his view. The message is resonating with voters, and polls indicate Melenchon is headed for a runoff against far-right leader Marine Le Pen in next year's presidential election.

"All we have to do is take the 18% held by the Bank of France and chuck it in the fire," Melenchon has said.

France's own prime minister has warned that reneging on the national debt would force the country to borrow at exorbitant interest rates, just as the government must turn to the bond market to raise more than $360 billion this year.

Melenchon insists his plan is feasible because it targets debt held by the central bank rather than investors. Still, at a recent campaign event, he hinted that debt cancelation might not stop with the Bank of France.

"Why did we make a single currency and an ECB together? We can do it and I bet we'd find allies in Europe," he said. "There is a debate — I'm not going after private creditors, not at this step in any case."

But the head of Germany's central bank, who also sits on the European Central Bank Governing Council, said Melenchon's debt-cancelation idea would be forbidden under the currency bloc's rules and could lead to hyperinflation. The prohibition reflects a founding principle of the euro: the bloc's treaties, shaped heavily by Germany's historical sensitivity to debt monetization, bar the ECB and national central banks from directly financing governments.

"No central bank in the Eurosystem nor the ECB is allowed to cancel national debt," Bundesbank chief Joachim Nagel told French newspaper Le Monde. "This would constitute monetary financing of government, which is prohibited under the European treaties."

Although the eurozone's biggest economy would stand in Melenchon's way, investors are growing more nervous about French debt. The yield on French 10-year bonds stood about 88 basis points above equivalent German yields, nearing the highest spread since Europe's debt crisis in 2012, when questions over whether the currency bloc would hold together drove borrowing costs sharply higher across the region's periphery.

Adding to the turmoil, there is no parliamentary majority that would support budget cuts to trim the deficit, which is near 5% of GDP — well above the European Union's sub-3% target and a source of additional bond market angst.

Kristian Kerr, head of macro strategy at LPL Financial, pointed to the spread between French and German 10-year yields as a key indicator, noting that 90 basis points has historically served as a ceiling during periods of fiscal stress. In a note on Wednesday, he warned that a decisive move above 90 basis points could signal that investors view France's fiscal challenges as long term rather than temporary.

"That shift would matter well beyond France," Kerr added. "European and global sovereign debt markets remain highly interconnected, and a material deterioration in confidence toward French debt could easily spill over into other countries with weaker fiscal profiles."

This story was originally featured on Fortune.com.