Alec Baldwin thinks President Donald Trump is ''an immensely dull man''.

The 61-year-old actor has been portraying the US leader on 'Saturday Night Live' since the 2016 election campaign but he admitted he shows a ''cartoon version'' of the former 'Apprentice' star because he isn't ''smart'' or ''engaging'' so if he went for something more true-to-life, it would send viewers to sleep.

He told Vulture: ''If we were looking for the most precise rendering of Trump's personality, you'd slow it down a lot. Trump is not really as energetic as I try to make him. There's a conflict there between a really effective impersonation of him and what I do.

''So what I gave them was my cartoon version of that. It's got certain gestures, it's got certain neuroses, it's got certain buffoonery and a kind of narcissism and so forth.

''But it is not by any means, nor could it be, a really precise impersonation of Trump.

''A long-form impersonation of Trump would put people to sleep in five minutes. Trump is dull. Trump is an immensely dull man. When you listen to him talk, he's not that smart, he's not that engaging, he's not that verbally skilled. He says the same thing over and over again.

''If we really did an impersonation of Trump, that would be the best sleep aid I've ever heard of in my life. So we did what I came up with, which was more of a caricature.''

The former '30 Rock' star recently admitted he thinks he is ''done'' with his celebrated 'SNL' impersonation.

He said: ''I feel like I'm done with that now. I'm so done with that.

''I mean, I had a lot of fun with [the cast] When Chris Kelly and Sarah Schneider wrote [Trump sketches in 2016 and 2017], that was new, it was fresh and the ratings were good.

''I can't imagine I would do it again. I just can't...They should find somebody who wants to do it. They're all my dear friends and I love going there, but the other thing is that I'm going to go to work this fall in a way I haven't done in a while.''