James Cromwell is
George Bush Snr
Aside from the impressive physical resemblance (tall, old, white hair), James Cromwell possesses the gravitas and presence necessary to convince as an elder Statesman like Bush Senior. He's already played Lyndon Johnson, Prince Phillip and US Presidents in The West Wing and The Sum of all Fears, so he knows the score - and earlier roles as military types should subliminally get across HW Bush's early military service.