"For those who are convinced that the prime minister is …some sort of poodle, it does not matter what he does," Sir David told the paper.
"You reach the point where if he had collected the medal, people would say that proves their point. But it's a much better - a much more complicated relationship - it's a two-way street."
Sir David also noted the importance of a British prime minister working closely with his or her US counterpart, as Mr Blair did with Bill Clinton and Margaret Thatcher with Ronald Reagan.
"The prime minister is listened to - but it's not like pulling the handle of a fruit machine. That is not how foreign policy works," he said.
Mr Blair was awarded the congressional medal after the invasion of Iraq and an address he made to Congress in July 2003, although the prime minister has waited 1,351 days to collect the award.
Sir David believes he may choose to visit Washington to collect his medal after his term in office comes to an end, widely thought to be later this summer after the Welsh Assembly, Scottish parliament and local council elections on May 3rd.
Click here to run an energy price comparison, and see if you could be paying less for your gas and electricity.