From 1972 to 1992 Delaware used a system of “challenge” primaries, in which a candidate for statewide office who received at least 35 percent of the convention vote could challenge the endorsed candidate in a primary. No such primaries were held in 1976.[1][2]
Glashan, Roy R. (1979). American Governors and Gubernatorial Elections, 1775-1978. Meckler Books. ISBN0-930466-17-9.
Gubernatorial Elections, 1787-1997. Washington, D.C.: Congressional Quarterly Inc. 1998. ISBN1-56802-396-0.
Scammon, Richard M.; McGillivray, Alice V. (1977). America Votes 12: a handbook of contemporary American election statistics, 1976. Washington, D.C.: Elections Research Center.