Have you noticed that TV ads for some politicians do not mention the candidate's party affiliation? Also, some ads may mention that a person is running for congress but the ads do not mention which congressional district.
Democratic candidates are terrified at being linked to Obama, which explains why you are seeing their campaign leaving out party affiliation, and as for the Republicans, by not mentioning party, they hope to cash in on the anti-Obama sentiment.
The political pundits are all predicting a big win for Republicans this November.
http://www.reuters.com/article/2014/10/19/us-usa-politics-obama-idUSKCN0I80V320141019 (http://www.reuters.com/article/2014/10/19/us-usa-politics-obama-idUSKCN0I80V320141019)