I don’t think there is a prescription for a political sketch to be successful, rather it is the outcome that can be defined. There are components of successful sketches, but what makes a good sketch is its effect.
What I am looking for as a result of reading a sketch – political or not – is in one sense ungraspable – relying on that old sense of I don’t know what it is, but I know it when I see it – but actually is at least for me solid although I am sure that solidity isn’t a comprehensive description of what a good sketch achieves.
When I started my own academic research I thought the aim was to discover something new and put it in an existing perspective. There remained some truth in that obviously, but I soon found that the majority of what I was doing was looking at what was already known (if not entirely understood) and putting it in a fresh perspective. And that is really the outcome I want from a sketch – taking something that I know or at least have an awareness of, and putting it in such a fresh light that I see it entirely differently. This is deceptive because I always keep in mind an observation coined by William Cowper (my memory may play me false here) that spoke volumes to me about the poetry of Thomas Gray. He wrote that what you discover in Gray’s work is things that you have never seen or understood before, but as soon as you read them, you feel they are so absolutely right, you have known them all your life.
It is therefore so easy to underestimate a really successful sketch.
I agree that sketches should be, if not actually funny, at least witty. They should be easily accessible to a reader while still having the odd challenging concept – my favourite example is that the Pilgrim Fathers didn’t leave England to escape religious persecution but to put religious persecution in place. Just like that phrase, a good political sketch should puncture current understanding, any self-importance and arrogance. They should point out foibles and inconsistencies. Finally I always think they should have a moral stance – though this is the element that I am least confident about in universal as opposed to my personal terms. To justify that I think a sketch should have a purpose and an objective and I would always want that objective to be derived from honesty, integrity and decency.
To summarise, I think it is generally understood that we all look ridiculous – well I do – standing naked just in our socks. What I require from a sketch is really just that – a vision of the ridiculousness of any of us once we have been stripped of pretension, pomposity and facade and any ways of achieving that will make a profoundly important sketch.