Complex sentence: By 1972, the amendment was supported by both major parties and was immensely popular; but though it made it through Congress, it was defeated when it failed to get the vote of thirty-eight legislatures by 1982.
Split into simpler sentences: By 1972, the amendment was supported by both major parties and was immensely popular. However, it was defeated in Congress when it failed to get the vote of thirty-eight legislatures by 1982.