Serious clashes off the Korean peninsula today, on Yeonpyeong Island. North Korea fired dozens of shells at the island, killing two South Korean Marines and wounding 18. The North said it was merely returning fire. South Korea acknowledged it had fired test shots in the area — but not into the North's territory. President Obama today called South Korea, quote, "one of our most important allies" and strongly condemned the attack. So tonight we ask you: What, if anything, should the U.S. do?