WHY it's scary:

Here’s the fear: Banco Santander, BBVA and the third largest bank in Spain, La Caixa, have combined assets of about $2.7 trillion. Spain’s GDP is just about $1.4 trillion.

In other words: Spain’s three biggest banks are nearly twice as big as the entire Spanish economy.

By contrast, America’s three largest banks by assets — JPMorgan Chase, Bank of America and Citigroup — have combined assets of around $6 trillion, or about 40 percent of U.S. GDP.  If JPMorgan , Bank of America and Citi are too big and too systemically important to fail, what does that make Spain’s big three?