Madrid’s trump card in this latest game of euro-zone poker is that the consequences of a Spanish default and exit from the euro zone would probably be so catastrophic that policy makers in Berlin will be willing to bend their bailout rules for Spain, and are on the verge of doing just that.

German officials have said they are prepared to weather a Greek exit from the euro if necessary, but no such claims are made about Spain. As such, Spanish leaders, who feel Madrid has already made many painful changes and spending cuts, are holding out for a deal that requires only a tightening of oversight on the financial sector and no strings attached to the country’s budget powers.

Spain also appears to be forcing a reckoning about the expensive steps political leaders in Europe need to take if they want to hold the euro zone together. Hopes that the European Central Bank would ride to the rescue, as it did with two waves of generous loans to Europe’s banks in December and March, or at the very least cut interest rates, now at 1 percent, were dashed when the bank’s president, Mario Draghi, said Wednesday that he did not “think it would be right for monetary policy to fill other institutions’ lack of action.”

“Some of these problems in the euro area have nothing to do with monetary policy,” Mr. Draghi said at a news conference, his message to European leaders boiled down to: “Your problem, not mine.”

The wrangling over Spain underlines the way the European Union stumbles to solutions for each problem as it arises. Frustration has grown over the uncertainty afflicting the global economy as a result of Europe’s instability and the toll it takes on an already slowing growth rate.