They were solidly on-board with Carter's Greenies and Pinkos back in the 70's until the Iranian Embassy crisis; that's when ABC News launched Nightline, as a kind of daywatch.
The MSM were all hooking it for Carter right up to the election; everyone was nonplussed when Reagan won so handily -- hell, it was a landslide. No incumbent since maybe Grover Cleveland had ever been blown out so hard.
The MSM talking heads were subdued until 1987, when they started cranking up for the '88 race .... and went all-out for the Dims until Dukakis collapsed, and then you could see the air go out of them until Clinton arrived. When Slick won, they started to see their chance to put America away forever, and they've been on a tear ever since.
I realize that the media has shown its left-wing stripes since Watergate, at least... maybe even earlier.
My parents gave me a subscription to Newsweek when I was in high school; I started reading it in the orthodontist's office, and enjoyed it.
Newsweek had a caption format for pictures back then that was interesting. Each caption was in two phrases, separated by a colon. The first part was factual, and the second part was more analytical, sometimes in the form of a question. The second part was in italics, too. I liked that, thought it was cool. Newsweek back then was pretty much down-the-middle. They covered campus unrest, but with a very slight underlying cynicism that I thought sounded like my parents.
That changed after Kent State; they began be a little less evenhanded. Their support for the students became a little more noticable.
Then, during Watergate, they began to really get into it. Newsweek had (IIRC) more than 50 cover stories about Watergate before Nixon resigned. When they got rid of Nixon in 1974, the media really started to get full of themselves.
I was aware that they supported Carter, but the intensity, the explicitness of their support was far less noticable then than it is today. You're right that that level of support began to waver with the hostage crisis; one might even say that it began to waver just a little bit when Carter admitted that he was shocked that Brezhnev had lied to him about Soviet intentions in Afghanistan.
They tried to support Carter during his election campaign, but their support was less than whole-hearted due to the obvious problems, the Iran hostages topping the list but others besides. The economy was a mess, with inflation noticable on a week-to-week basis and the prime rate over 15%. The misery index was a staple of the nightly news, and there was no escaping it.
I agree with you about the sea change that happened during the Clinton campaign. They completely stopped even pretending to be objective; that all went right out the window. Clinton made them giddy, made them act like teenage girls. When Bush 41 lost, they practically started dancing the jig on camera.