I thought it was clear I was asking for examples of precedent in relation to the actions of the executive branch, not for reactions to it. Orders of magnitude say a lot about the resistance that was building against Trump since before he even took office, but they tell us exactly nothing about what the man has actually done.
Let's unpack the rest of your examples, using two simple metrics: a) is the claim actually unprecedented? b) is the precedent meaningful within the context of this discussion (i.e., does the precedent significantly alter, or stand to significantly alter, the functions of the executive branch in relation to either other government offices or the American public at large)?
Not releasing tax returns.
a) This isn't unprecedented. Gerald Ford didn't release his either.
b) This isn't meaningful given the context. A presidential candidate isn't required to release his tax returns, so inferring some sort of nefarious intent in declining to do so is about as sophisticated as saying "if you have nothing to hide, then you shouldn't care about your privacy."
Weird Russian ties resulting in the resignation of Flynn
a) First, let's clear up exactly what you mean by "weird Russian ties", since that doesn't convey much. Flynn had a telephone call with a Russian ambassador, in the course of which Obama's recently imposed sanctions against Russia for the DNC hacking came up. Flynn suggested (not promised, according to the intelligence official who was tapping the phone call) that Obama's sanctions wouldn't necessarily carry over into the new administration.
That's it. That's the sum total of all the ZOMG RUSSIAN TIES!!! media headlines you undoubtedly saw for a week straight. Now, the only thing Flynn is potentially guilty of in having had this discussion with a foreign diplomat is violating the Logan Act, which states a private citizen cannot conduct diplomacy on behalf of the United States.
This is neither unprecedented nor particularly meaningful.
The "betrayal" and firing of the attorney general
Again, this warrants some clarification (you'll notice an ongoing theme here. This is what happens when you seek to discuss current events from a level any deeper than drive-by rubbernecking).
Firstly, Yates was the acting attorney general, left over from the Obama admin, who was biding her time until Trump's appointment was confirmed. This matters because firing someone from a position you appointed them to rather than one they temporarily hold from legacy signals something entirely different (see: the media coverage of Flynn vis a vis the internal state of the Trump admin).
Secondly, while "betrayal" may touch on the melodramatic, it's not really inaccurate. As AG, Yates was obligated to fulfill the duties of her office, even when that meant enforcing executive orders she didn't like. Her own department had determined that Trump's order was legal, so her rebuke of the order was a rebuke of her own department.
a) This, too, is not without precedent. Nixon canned his AG.
b) Nor is it meaningful within the context, for the reasons already provided above.
Historically low popularity ratings
a) This is true, at least as far back as Gallup polls go (1940s).
b) However, it's not particularly meaningful for our context here. Again, reactions != actions.
Calling the free press the enemy of the American people
a) Most likely unprecedented.
b) Very meaningful, but not in the manner you think. The media is an enemy of the American people in that they have been asleep at the wheel of their journalistic responsibilities for the last 8 years, and have only now woken up to the terrifying headlights of the Mack 10 truck barreling down at them full speed. What's most precious about this point is that even now they aren't really doing their jobs because they're too busy tripping over themselves to lash out at Trump the brand.
His "victory" with the largest popular vote loss in history
a) This isn't unprecedented (others have lost the popular vote but won the election), but the degree to which Trump lost the popular vote is the largest.
b) This, too, isn't particularly meaningful. We have this thing called the electoral college. I realize a lot of Americans woke up on November 9 and looked up this process for the first time in their adult lives (and now, surprise, they're calling for the system to be changed! Isn't it adorable?), but for those of us whose attention span stretches beyond the last decade, there is nothing about this that's particularly noteworthy. Just because you don't like the person who's in charge now doesn't mean the system failed you.
I agree that he's embarrassing, clownish and cringe-worthy. I did not, however, state that he is a bad leader. I don't believe anyone can make such a statement when the man has only been in office for a month. It would be quite prudent for all of us to pause, catch our breaths, and evaluate Trump based on how he actually performs in the White House over the next 4 years. Maybe he'll live up to the staggering amount of negative hype and crystal ball-gazing that so many of us have been doing lately. Maybe he won't. That remains to be seen.
The important point here is that, as others have put it, too many grown adults are quite literally freaking out over Trump's presidency without having the required sociopolitical acumen to justify not only why they're freaking out, but over what. Travel bans that aren't substantively different than previous orders, transgender bathrooms, lewd remarks caught on tape--none of that is truly important, not if you really care about issues of government and liberty. That's the fluff. That's the shiny bauble that distracts people from recognizing that regardless of who's in office, none of them really care about you and me. They're all of them supporting their own brand.
The precedent for that was set a long, long time ago.