President George W. Bush said Friday defense secretary Donald Rumsfeld enjoys his full support and that Rumsfeld's leadership of the Pentagon was "exactly what is needed at this critical period." Bush issued his statement to counter the intensifying calls for Rumsfeld to resign because of criticism that the defense chief has mishandled the Iraq conflict and made other mistakes. Bush wrote that he discussed ongoing military operations with Rumsfeld earlier Friday, "and I reiterated my strong support for his leadership during this historic and challenging time for our nation." The defense department has been given many difficult missions, and "I asked Don to transform the largest department in our government. That kind of change is hard, but our nation must have a military that is fully prepared to confront the dangerous threats of the 21st century," Bush said. "Don and our military commanders have … been tasked to take the fight to the enemy abroad on multiple fronts," Bush wrote. "I have seen first-hand how Don relies upon our military commanders in the field and at the Pentagon to make decisions about how best to complete these missions." "Secretary's Rumsfeld's energetic and steady leadership is exactly what is needed at this critical period. He has my full support and deepest appreciation," Bush said.