I think it's evidently true that mass media can make or brake politicians/parties. Corporate owned media like Viacom and News Corp (Rupert Murdoch's empire) favour right wing policies and promote it via their news outlets, mostly by supporting politicians that favor their politics and undermine politicians who do not share their believes. So let's look at the British context in this matter.
One thing that comes to mind is selective portraying of news. There has been a lot of focus on Jeremy Corbyn's perceived lack of decisiveness in curtailing anti-semitism in the Labour Party, which has partly cost him the elections. This is not entirely wrong, as he was not very authoritative as a party leader in dealing with this issue, though he proved to respect Jewish people in his activist days. However, under Corbyn's leadership, the Labour party has actually opened an investigation on anti-semitism within the party, installed policies to better protect Jewish party members and fired those who openly expressed anti-semitic views, like former London mayor Ken Livingstone.
What really grinds my gears is that Right wing, Conservative politicians like Boris Johnson have actually said horribly racist & xenophobic things and get away with it, e.g. calling people from Africa ''Piccaninnies'' and ''Watermelons'', gay men ''tank-topped bum boys'' & that Islamphobia is a ''natural reaction'' to Islam. And then I have not even mentioned the raging islamophobia within the Conservative party, which the party has openly denied by sweeping a report on this issue under the rug.
And yet, major newspapers, mostly owned by News Corp, like The Mirror, The Sun, The Telegraph & The Times kept pushing the frame that the Labour Party is racist, while ignoring the same issue that is clearly visible for all to see when we look at the Conservative party.