Complex sentence: After ordination, Sussman remained at HUC until 1987 when he earned a Ph.D. in Jewish History under the direction of Jacob Rader Marcus, the most senior scholar of American Jewish History, and Jonathan D. Sarna, who is currently at Brandeis University.
Split into simpler sentences: After ordination, Sussman remained at HUC where he earned a Ph.D. in American Jewish History in 1987. He studied under the direction of Jacob Rader Marcus, the most senior scholar of American Jewish History, and Jonathan D. Sarna, who is currently at Brandeis University.