This is one of those cases where the episode does not take place around the same time as it was broadcast. Ronald Reagan was elected in 1967 for two consecutive terms ending in 1975. So he wouldn't have been running again until 1970.
Either this episode took place before the 1967 election, two years before the broadcast, or it was a look into the future at the events a year later.
I don't want to play hob with the entire timeline for 'The Lawyers', which debuted with two pilot movies at the end of 1968 and in March of 1969. It began it's three season run in September of 1969. And since the overall premise of the show began in 1968 with Walter Nicholls hiring the two Darrell brothers to help with his workload, I really can't push the show back a year to 1967.
Better to consider "Shriek of Silence" to have been from the show's future, a year later than it was broadcast. Stephen Patterson was going to run against Reagan in the 1970 election.
(One other idea that I rejected - that in Earth Prime-Time, the election cycle is different from that in the real world. Such an idea works for the TV dimension which houses 'Smallville', 'The West Wing', and 'Mr. Sterling'. But I'd rather keep that aspect aligned with the real world since so many TV shows could have episodes thematically timed to various elections.)