During an interview on NBC’s Meet the Press on Sunday, Mr Mullen discussed the importance of the peaceful transfer of power and the impact of Donald Trump’s delay of the official transition process.
“I think I'm actually very concerned about the Trump loyalists who have now gone to work in the Pentagon,” Mr Mullen said, suggesting that they could cause issues for Mr Biden during the transition period.
“I mean, recently, Secretary Esper was fired, and a host of other people left the building. And there are some real Trump loyalists there now in charge and it's pretty difficult to think that over the course of 50 or 60 days you can do something constructive, but you can do something that's really destructive," he added.
Mr Biden was declared winner of the 2020 presidential election by news networks on 7 November but Mr Trump delayed the official transition process after he refused to concede.
Mr Trump took to Twitter on 23 November to finally announce that he had given GSA head Emily Murphy permission to work with Mr Biden’s transition team “in the best interest of our country”.
During the interview Mr Mullen considered Mr Trump’s attitude towards the transition in comparison to George W Bush and former President Barack Obama, fearing that the delay could have an impact on national security issues.
“One of the things I learned in the job that I had is you don't want to, you'd like to do all you can to not box in the president - to give any president as many options and as much space as possible. So, this is obviously the opposite case right now,” he said.
“It appears that the current administration is trying to lock in as many options as, as many issues as possible to make it much more difficult for President-elect Biden to govern. And actually, historically, that has just never been the case.”
Mr Mullen expressed “worry” over the timing of the difficulties given the ongoing coronavirus pandemic and the state of the economy.
“National security issues do not wait, it's going to be a particularly difficult transition in that arena, actually having started three weeks late.”
The move from the White House to start the transition process came just hours after Michigan formally certified its election results just days after Georgia.
A number of Republican senators, including Alaska’s Lisa Murkowski and Ohio’s Rob Portman, had turned on Mr Trump and called for the transition to begin to ensure a smooth handover to Mr Biden before he is scheduled to take office in January.