The first 100 days of a president’s term offer a sense of the direction a president will take and a window on how he will cope with his vast responsibilities. But it is the period after — particularly the second 100 days — that can set the tone for his term and foretell its success or failure.

President Barack Obama has already made a sharp departure from President George W. Bush, signaling a wholly new approach on taxes, abortion, embryonic stem-cell research, international relations and government involvement in the economy, among other issues.

Much of what he has achieved so far has been done by executive fiat or as part of a one-time economic stimulus package rammed through Congress in February.

But over the next 100 days, Obama must show that he has the stomach to implement policies and forge legislation that will have lasting effects.

History shows the next moves he makes could define his presidency.

And, while he will have to make sure that the economy continues to recover if he hopes to be re-elected, the defining issue for Obama will be health care.