European stocks tumbled Wednesday after Standard & Poor's downgraded its debt rating on Spain, compounding sovereign debt fears just as a resolution to the implementation of Greece's aid package seemed to be in sight. The news hit the euro, pushing it down to a 12-month low. Standard & Poor's downgraded Spain one notch to double-A from double-A-plus and kept a negative outlook. The ratings agency also said Spain would likely see an "extended period of subdued economic growth" and cautioned that it could face another downgrade.