News media report results. News channels reflect the inherent bias of their owners. Professional journalists who work for news media companies are expected to follow standards. However, everyone has a bias, and it is human nature for that the occur.
Some news channels are blatantly biased. For instance, Fox News, which is owned by Rupert Murdoch is conservatively biased. While their creed is "Fair and Balanced," Fox is anything but that.
NBC, as another instance, is supposed to protect objectivity. However, it is clearly liberal.
Public Broadcasting is expected to toe the line as being most objective. Their reports often aggregate polls and broadcast the average.
Donald Trump declared that all polls are being manipulated to defeat him. That is simply impossible.