The 'What To Expect When You're Expecting' actor took on the part of the former US president in 'The Special Relationship' but admits he almost turned it down because there was such pressure on him to get it right.
He said: "That was probably the scariest thing I've ever taken on. I almost turned it down because I knew Bill and I just couldn't understand why they wanted to cast me in it. It was daunting because he was one of the most famous men in the world, but that was the reason I decided to jump. I always find that fear is the greatest motivator – it really does get the juices going!"
Although he had met the politician, Dennis says he didn't get any advice from the former leader once he had signed up for the film.
When asked if he spoke to him, Dennis told Total Film magazine: "No, not once I got the role – everything shut down from there! But he really was one of the most fascinating people I've ever met in my life."