And today we do face serious new challenges in the area of defense policy.

Yet perhaps the President's most serious political challenge is now being posed by his own party.

This fall the Republicans hope to provide a more serious challenge.

By the time I met him in mid-1994, though, his authority had come under serious challenge.

America is under serious challenge now, in another struggle we must win - and will.

Look, we're going to face some serious new challenges in the next four years.

Yet, our health care system still has many serious challenges ahead of it.

The first serious challenge of this new government is to bring the budget under control.

On the other, without change, they face a serious challenge.

But they also add a lot of serious challenges to our work.