As the bank runs low on cash, the Italian government is stepping in to help, with plans to inject as much as 20 billion euros into Monte dei Paschi and other troubled lenders. European regulators gave their preliminary approval to the Monte dei Paschi deal on the condition that the bank go through an in-depth restructuring and its finances pass muster.

Much of the reform instituted after the 2008 financial crisis was intended to prevent banks from becoming so big and so risky that they could hold the global economy hostage. Politicians and policy makers didn’t want taxpayers to be on the hook for the banks’ mistakes.

Under the new rules, national governments are not supposed to inject fresh taxpayer money into a bank if it is deemed insolvent. When a bank gets into financial trouble, shareholders and bondholders, assumed to be sophisticated investors aware of the risks, are supposed to take the hit and bear the losses.

The health of Monte dei Paschi — which will be assessed by the European Central Bank as a condition of the deal — will be a crucial measure to ensure the bailout follows the rules. But the finances of Monte dei Paschi are open to significant interpretation, putting the rescue in a regulatory gray area.

The central bank said in late December that Monte dei Paschi would need €8.8 billion to plug a shortfall in its capital. The Italian bank lost €3.4 billion last year as it had to set aside more reserves for troubled loans, and it continued to bleed money in the first quarter.