There was a time when more people where informed/cared. Somewhere between western expansion of literacy and mid 20th century.
If people really were concerned why do they keep electing people who are tied to big money?
Sound bites and catchy phrases have always been around, it is easy to associate a person with a popular +/- slogan.
As an example:
In 1900 (right in the middle of the time you have referenced), there were 357 Representatives in the House, for a population of 76 million. Making each Representative represent (on average) 212,885 people (about twice as high as I would prefer.)
In 2015, there are 435 Representatives for a population of about 319 million. Each representative represents (on average) 733,333 people.
So, in 2015, our representative represent over 3 times the people in 1900. So, each voter has less than a third of the influence of any voter in 1900.
This is, of course, without also noting the massive increase in the power of the federal government that has accompanied the diminution of accountability to the voters.