Are Bernie Sanders supporters overstating how much media bias there is against him?
Probably. Due to confirmation bias, it's almost guaranteed that anyone with a horse in the game will notice every example of bias against their candidate, and downplay bias towards their candidate and against the others. In that spirit, here's my view of it, as someone who likes Bernie but supports Clinton.Things that definitely aren't bias Some complaints are bogus and results of wishful thinking/the fact that Bernie is the underdog. For example, a common complaint is that the media called more states early for Hillary. They did that because exit polls showed she was winning those states by large margins, which meant that it was very safe to call the state, based on the historic track record for exit polls. When Bernie won a state (Vermont) by large margins, they also called it immediately for him.Additionally, a lot of the complaints are simply complaints that his odds of success have been consistently understated. For the most part, however, these have been based on polls, which have, with the exception of Michigan, been pretty accurate. Reporting, for example, that Clinton is likely to win VA isn't really bias if she actually does win VA. Polls aren't perfect (see Michigan), but those relying on polls have generally been better than the pro-Bernie pundits (e.g. Bernie Sanders Will Win the Democratic Nomination and Presidency in a Landslide).Things that could be bias: Amount of Coverage: This is probably the most subjective measure, because there's no objective standard on what's the right amount of coverage. Just because Bernie is running, that doesn't mean he's entitled to equal attention. They didn't cover O'Malley or Chafee as much as they did Sanders, because Sanders had more support than them. Similarly, Clinton has always been the favorite for the election: at very few points has it looked like she was going to lose the primary. Among people willing to put money on the line to guess Bernie's odds, he's never been at better than 20% odds (2021 President - Democratic Nomination ‡ more recently it's down to about 5%). Sanders supporters who disagree with that either a) have a really good investment opportunity on betting markets or b) should take a careful look at their cognitive biases. If Clinton is the likely nominee, then that means that she's inherently more newsworthy. I personally think Kasich would be a better nominee than Trump or Cruz, but he's extraordinarily unlikely to win the nomination, and therefore it's less important to learn things about him. Should news media actively start covering Kasich as much as possible? Probably not. You can measure how much coverage Bernie has got against the other candidates, (see Measuring Donald Trump’s Mammoth Advantage in Free Media), and you can make your own judgements on exactly how much would be fair (somewhere between it would be fair to cover him 5 times less than Clinton because that's he's 5 times less likely to be president, or just as much, because he's the only other candidate: the actual answer is about half as much), but there's not a really simple answer to this. On top of this, not all news is good news. For example, Trump has received tons of free media, but the net result has made him less popular in the general election.I also think there's a reasonable point that Sanders's consistency plays against him here. You can only run so many "Sanders decries rigged system and calls for political revolution to cheering crowd in full stadium" stories. He'd probably get more coverage if he made dick jokes and harassed people, but see above point about not all coverage is good coverage.Things that are definitely bias: That said, there's obviously some bias against Bernie out there. In general, I think the crime is that it's frequently a dismissive (probably because they're focussed on his odds of winning and ignoring the equally newsworthy story that he's popular). This isn't just Bernie-supporters saying so: I think the NYT public editor does a good job highlighting this in the NYT (see Were Changes to Sanders Article 'Stealth Editing'?, and Has The Times Dismissed Bernie Sanders?).Of course, some times articles critical of Sanders are deservedly so. If your numbers don't add up, that's something worth being brought attention to. It's not media bias to ridicule the claim that single-payer will save more money on prescription drugs than is currently spent on prescription drugs. Study: Bernie Sanders's single-payer plan is almost twice as expensive as he says. I think Bernie supporters do their cause a disservice when they dismiss criticism out of hand based on media bias. If your definition of media bias is anything not completely flattering of Bernie, than it's you, not the media, that's biased.