Complex sentence: While serving his sole term in Congress, from March 1847 to March 1849, Lincoln brought his model with him to the offices of Zenas C. Robbins, patent solicitor, who most probably had drawings done by Robert Washington Fenwick, his apprentice artist.
Split into simpler sentences: While serving his one term in Congress (March 1847 to March 1849), Lincoln retained Zenas C. Robbins, patent solicitor. Robbins most probably had drawings done by Robert Washington Fenwick, his apprentice artist.