Yes, and that's why the party identification is important. If the ID breakdown is significantly different than recent comparable elections, you have to at least consider the effect on the outcome of the poll.
("Push polls" become obvious when you consider this metric. Some pollers conduct these "polls" to reinforce a pre-determined outcome, and make their candidate look good.)
And, you have to consider whether this is a registered or likely voter sample. At this point, registered vs. likely is probably meaningless, because I don't know how one can reliably measure that 5-6 months early. But, it can be a useful measurement of voter enthusiasm.
But, since a random phone poll only uses people that accept the call, it tends to over-sample people that are at home and answer the phone. This almost always oversamples Democrats.
I think one of the big stories 50 years or more from now is just how corrupt the media is. I work in the media, but I am ashamed of how biased the media is in general.
Of course, the media has always been biased - yellow journalism in the 1800s, etc. Nothing new but it is so pervasive and blatant.