But with Europe veering toward recession and with increased skepticism that discipline will solve the deep structural imbalances in the euro zone, the markets’ concerns have passed from doubts about the solvency of individual countries to fears for the euro zone as a whole. Those doubts now include Germany, which cannot by itself, even if it wishes to, guarantee the credibility of Italian and Spanish debt, which totals more than $3.3 trillion.

For Kenneth S. Rogoff, an economics professor at Harvard, the biggest problem for the euro is not money so much as structure, or the lack of it. “This is a deep constitutional and institutional problem in Europe,” Mr. Rogoff said. “It’s not a funding problem.”

Yet, with even German interest rates rising, the markets are now worried about the sustainability of the euro zone as a whole, said Simon Johnson, a former chief economist for the International Monetary Fund and a professor at the M.I.T. Sloan School of Management. “The market has signaled that the risk is relative currency risk, not sovereign risk,” Mr. Johnson said. “So a ‘big bazooka’ won’t work for Europe now, because of worries about the euro itself breaking up and German interest rates going up.”…

If so, Mr. Rogoff said, “the Europeans can stretch it out a long time, they have the money.” Nevertheless, he said, they “need to take a big step toward economic and political union, whoever wants to be a part of it.” Germany “is right to hold out for systemic changes,” he said. “The Europeans hoped to have 30 to 40 years to integrate more fully. Right now they don’t have 30 to 40 weeks.”