What in the world does this have to do with right or left? We're talking about a musical performance, for Pete's sake!
Sifting through recordings of Copland's Lincoln Portrait
(1942) is a great way of reminding ourselves what it was like when music-lovers weren't so averse to mixing music and politics (not so long ago!). You can always tell which performances are a product of the pre-McCarthy spirit, when Copland could be open about his Leftist leanings, and which are a product of the Communist clampdowns of the late 40s and 50s.
The giveaway line is the bit about "of the people, by the people, for the people." A post-McCarthy narrator will usually read the line thus: "OF the people, BY the people, FOR the people..."
A Coplandite narrator will usually read the line thus: "of the PEOPLE, by the PEOPLE, for the PEOPLE!"