Nixon is really more of the supporting part here, But good as Shannon is, it's near impossible not to be riveted by Kevin Spacey who was (not surprisingly) tremendous. He's probably the best “Nixon” I’ve seen. Human, but not to the degree of making him “likable.” Very awkward in a believable way. He’s got the voice and body movements down pat. It's not a caricature, but a rich performance.
Rather than show the trailer (which tries to emphasis how ludicrous it all is), I think the featurette gives a much better sense of the film and has some very good commentary, including by the real Jerry Schilling, the longtime friend of Elvis who accompanies him on the trip (and later went on to briefly manage a young Billy Joel and the Beach Boys).