Originally Posted by MightySmurf
Here's what wikipedia has to say about Bert Cooper:
Bertram "Bert" Cooper (Robert Morse): The somewhat eccentric senior partner at Sterling Cooper. He leaves the day-to-day running of the firm to Sterling and Draper, but is keenly aware of the firm's operations. Like many of his executives, Bertram is a Republican. He is fascinated by Japanese culture, requiring everybody including clients and his sister (a shareholder) to remove their shoes before walking into his office (which is decorated with Japanese art). He is a fan of the writings of Ayn Rand and implies he knows her personally. Among his eccentricities, Bert frequently walks through the offices in his socks and intensely dislikes gum and smoking (an oddity for the time, especially considering that Lucky Strike cigarettes is a major client). He owns a ranch in Montana and is a widower with no children. Don approaches him about buying back the agency at the end of the third season, which evolves into them forming their own.
I'm pretty sure all the characters in the show are republicans. Considering Draper, Sterling, and Cooper's push to become campaign advisers to Richard Nixon, and during the election when Betty Draper says, "I just don't trust that Kennedy fellow." And goes on to say some nice things about Nixon.
Also, the political adviser that Betty leaves Don for was talking about jumping on the campaign for Nelson Rockefeller for the future 1968 Republican Primary.