If he wore a tuxedo, would that be Benedict's cummerbund?
As for Obama: How about Denzel Washington?
I think Denzel Washington brings a certain fire to most of his performances. He often plays characters who are fundamentally angry in some way. You always get the impression watching his performances that he's hiding a caged tiger just waiting to get out.
President Obama is not that kind of guy. If anything, that's one of his biggest political liabilities -- he's so cool and aloof that sometimes he has trouble connecting emotionally with the electorate. He's a very Keep Calm and Carry On, Stiff Upper Lip sort of guy. So Denzel Washington wouldn't be my first choice for playing President Obama.