If the panic were confined to these three, the euro zone could cope.

ECONOMIST: The euro crisis

But it also risks triggering depositor panic across Europe's weaker banking systems, something the euro zone spent most of 2012 trying to avoid.

WSJ: Post-Election Inaction Could Reawaken Crisis

But as troubled euro-zone member Cyprus reopened its banks Thursday, there was little sense of panic, which calmed investor nerves and set the stage for the index's push into record territory.

WSJ: S&P 500 Breaks Record