Interesting bit of history that I wouldn't remember because I was born in 1954.
Lyndon Johnson was rumored to have won his senate seat by fraudulent votes in 1948. This earned him the nickname of "Landslide Lyndon." Some things never change I guess. Who knew they were fighting over votes in 1948?
During his run for re-election in 1954, he ran into some problems with anti-communist groups who resented his liberal agenda. This is what gave rise to forbidding politics in churches, although his main target was actually to stop nonprofit groups. Johnson had to stop these people from destroying his political future.
Johnson inserted language into the IRS code that prohibited non-profits, including churches, from endorsing or opposing candidates for political office.
Many people felt and still feel that this is a violation of the First Amendment of the Constitution of the United States.
Personally, I do not believe that political issues should be taught from the pulpit during a worship service because that is not the purpose of the pulpit and robs it of its sanctity. Isn't the pulpit on the altar? Isn't the pulpit a podium where God's word should be studied?
"Render therefore to Caesar the things that are Caesar's, and to God the things that are God's." (Matthew 22:21 RSV)
I do, however, feel that like minded individuals should be able to have meetings, even at the church, to discuss political issues. We should be free to congregate and discuss anything at all, wherever we wish, within reason.