Cornwell held the rank of
Major and later
Colonel, as a staff member under both King
Kalākaua and Queen
Liliuokalani. She had chosen these men specifically to support her plan of promulgating a new constitution while the legislature was not in session. Publisher and philanthropist
Thurston Twigg-Smith, the grandson of annexation leader
Lorrin A. Thurston, made the case that Cornwell was part of a royal inner
cabal of the queen's own cabinet ministers who worked to oust the monarchy. She attempted to promulgate a
new constitution, but Cornwell and the rest of the cabinet were either opposed to or reluctant to sign the new constitution. Their opposition was one of the causes which ultimately led to her
overthrow by the
Committee of Safety headed by Thurston. After the overthrow, Cornwell and the rest of the Parker Cabinet were removed from office. After the overthrow of the monarchy and the annexation of Hawaii to the United States, Cornwell became a member of the
Democratic Party and served as a delegate to
1900 Democratic National Convention for the
Territory of Hawaii. He died at his home at
Waikapu, Maui, on November 18, 1903, of heart disease. ==Personal life==