Prime Minister Shinzo Abe managed to achieve half of the two critical goals he set for Thursday's summit with U.S. President Barack Obama: He succeeded in getting America's pledge to defend the Japan-administered Senkaku Islands, a vow likely to keep China in check.

But Abe failed to achieve the other goal, namely a broad agreement on the Trans-Pacific Partnership talks. This was also a setback for Obama, who lobbied hard to seal the free trade deal. The two were thus unable to issue a joint statement after their talks.

But the security vow was significant.