Time-Warner owns CNN. Time-Warner donates significantly to Hillary's campaign. Time-Warner, therefore, has a stake in making Hillary the nominee for the Presidency and has no problems using its ownership rights over CNN to increase the odds of that investment--because that's what donations really are, investments into an enterprise in return for a stakeholder position--paying off. This media outlet flat-out lied about Hillary's performance, down to putting a CIA asset on the panel of questioners and moderators, to make this happen.
This is hardly unusual. It's standard practice, as Herman & Chomsky noted in Manufacturing Consent decades ago, and therefore not illegal until it meets the standard of defamatory slander or libel. Half-truths, edited audio or video, etc. to create the desired Narrative is well within the statutory code for media outlets purporting to be news outlets. Mainstream news is really entertainment. It's why there is no difference between Entertainment Tonight and NBC Nightly News, right on down to using green screen tech to fake being on location.
Not that any other candidate is clean; their campaigns are all doing Narrative Warfare, so it's more a matter of who's lying least and how than who is or is not lying to get their way. You can't rely on the mainstream media to inform you properly; each corporation has a stake in the outcome, so they will slant their coverage to favor who they want to win. (Yes, this applies to the GOP as much as it does to the Dems, and the shut-out of all other parties is the same thing on a larger scale.)
Don't expect a lot of alternative media to do the job either. Some are incompetent, some are compromised, and some are astroturf fronts. Only a few are properly independent as well as committed to proper journalistic best practices, so I would--again--recommend that you development the Trivium Method so that you can rely on your own prowess of mind to sort through this bullshit and discern who you should support (if any) and how.