There is many choices on the web and the best political forums are those where you
feel comfortable knowing you may express your views and could become involved in positive arguments with your fellow members without being personally attacked. The discussion board can have an active membership with regular new posts and people available for discussion. There will probably be a variety of new threads opened at least on a weekly basis. Politics is a fast paced subject and nobody wishes to belong to a community forum, political or otherwise that nobody posts in.
When you join a new membership webpage always be sure to understand the rules and abide by them. Otherwise you can find your very own posts being deleted and in severe cases you could be asked to leave. Have a read through the posts to see if the threads become an interesting dialogue or merely an argument - the web version of a shouting match. Political forums are by definition someplace where people will go to argue. So it's good not to be extremely sensitive about the replies one of your own posts could get. However, if the particular person answering has launched a personal attack on you as opposed to entering into a positive argument, you should not respond in kind. It is best to inform a moderator or the forum owner who should handle the issue.
Politics covers such a diverse range of topics that it is possible to be a Democrat yet hold really different views on a particular issue to a fellow Democrat. Fortunately we live in a culture that promotes freedom of speech and provides you a chance to talk about your very own outlook without fear of punishment. But sometimes people take advantage of this freedom particularly in web political forums where they can register without revealing their true identity. They can hide behind their call handle and make use of the membership website as a way to vent extreme point of views. A well moderated community forum will normally do their best to stamp out this sort of behavior.