Washington (CNN) -- Adm. Michael Mullen, the chairman of the Joint Chiefs of Staff during most of Robert Gates' time as secretary of defense, said Thursday that it won't be easy for the new defense secretary to match his success.
"When you look at what he achieved, at some of the number of programs that he has been able to both propose, recommend and ended up being eliminated, it's the best work I've ever seen. So from my perspective, he has set a pretty high bar," Mullen told defense reporters. "I think it's one (thing) that the next team is going to certainly have to both deal with and figure out how to equal if we're going to get this right."
Gates is scheduled to retire at the end of the month. President Barack Obama has picked CIA Director Leon Panetta to replace him and wants Gen. David Petraeus to take over at the CIA. None of those nominations has been confirmed by the Senate yet.
Mullen also answered several questions about Pakistan and the impact of the U.S. raid that killed Osama Bin Laden. He said Pakistan is in the middle of an "introspective review" of its relationship with the U.S. The country has already asked the U.S. to remove hundreds of military trainers from missions.
"They're going to have to finish that (review) before we get back to a point where we're doing any kind of significant training with them," Mullen said.
Mullen was clear that now is not the time to end U.S. relations with Pakistan, though.
"What I worry about is, should we get to the point where we walk away in the future, then, 10 years from now, 20 years from now, we go back and it's much more intense and it's much more dangerous. We're just not living in a world where we can afford to be unengaged in a place like this."
As far as the upcoming reduction of U.S. troops in Afghanistan, Mullen said that Petraeus, the coalition commander in Afghanistan, still has not sent his recommendation to the Pentagon.
"It's still really in his hands, if you will, and his recommendation will kick off the process. Certainly, we're all aware that it's - that the president has committed to a decision to start in July. So we think the process will move forward here rapidly, certainly in the next few weeks," Mullen said.
Whatever the recommendation is, the final decision won't be easy.
"We've had more discussions about process than we had, you know, "Here's the answer," because we don't know what the answer is," he said. "In the end, this is a decision for the president and nobody else, and he will - I'm sure he will make that."