Dubin, p. 657. Dubin has the wrong Democratic nominee (Robert B. Holmes). I checked the New York Times, which ran a story on 11/6/1966 about the Hatfield surge at the end of the campaign.
This race was one of the surprises of 1966. Gov. Hatfield began the race far behind in the polls. Sen. Morse recruited Howard Morgan to run in the primary on the Democratic ticket as a specifically anti-Vietnam War candidate to counter Robert Duncan, a supporter of Pres. Johnson's Vietnam policy. Duncan won the primary easily and becam the immediate favorite in the general election race. However, just before the election, Pres. Johnson cancelled an appearance with Duncan and Hatfield managed to win by a narrow margin.