But perhaps to counter the concerns of critics wary of his reservations about American military involvements abroad, Mr. Hagel offered reassurance. "America does not have the luxury of retrenchment," he said. "We have too many global interests at stake, including our security, our prosperity and our future. If we refuse to lead, something, someone will fill the vacuum. The next great power may not use its power as responsibly or judiciously as America has used its power over the decades since World War II."