For me the voice is the most important, but making your singing believable makes a great performer.
The Democratic chairman doesn't need to be a household name. Most people didn't know who Ron Brown was when he was chairman of the Democratic Party, but he put the party in a position where Bill Clinton could come in and he had a solid base to run from.
There's definitely a wave of Brits doing great work on American television, and I wouldn't mind being one of them!

