While there are things that are just executive or judicial--and Congress has a tendency to assume that they're the royal family and there is no actual king to overrule any of them at times, so there are hundreds of de facto kings--very often the problem is what Congress has done.
So the ACA was largely left unwritten. The executive branch was charged with writing the regs for it, things that probably should have been legislated. At the time this was discussed and it was considered necessary in order to get the minimum number of votes necessary to pass a set of controversial provisions in the law. Even when it came to money, the assumption was that the administration would cough up millions of dollars that were assumed necessary but not allocated. Why did they do that? Because they needed the fiction that it was "budget neutral" against the budget prediction that was originally proposed--it might have additional costs, but it would cost more above those additions, and some Congressional votes depended on not falsifying that fiction. Even if it meant taking student loan savings and using the sale of some timber by-product as part of the health-care savings that would fund the ACA. Everybody was convinced that the arc of history had bent appropriately so that the proper people would stay in power, so the regs and the funding were in the bag. He's doing what the laws allow. It's like Obama and the DOMA or immigration law: Obama undermined both sets of laws because there was space in the text for him to legally do things, even though it's not likely that they'd pass an "original intent" or "original spirit" of the law test. Apparently faithfully upholding the law means "enforcing above and beyond the letter" or "seeking to undermine", depending not on the law's status but on what's politically desired at the time. The laws are a Rorschach test of sorts, not a legal codex.
Or take the national emergency legislation. We have a lot of national emergencies currently in place. We've parodied standard practice in requiring that a "national emergency" be some sort of invasion or widespread problem inside the US, but that's either a out of ignorance or through intentional deception. While some might involve disease or something else domestic, few do. It takes 60 seconds or less to see the range of them, how they're used, and how they're abused. You'd expect Congressfolk to have done at least that amount of footwork, or to have farmed it out to staffers if it was too onerous. There's no good follow up to that sentence, so paragraph break.
Certain sanctions against Iran are still imposed (and changed from time to time) under an emergency from 1979. There are sanctions still in place and enforced against some Zimbabwe ex-leaders long since out of power over a food crisis that ended over a decade ago. It's hard to argue that Bunyoni and Bizimana constitute real threats of violence and mayhem in the US that could upset the national order in the US and create chaos and disruption, but for the last 4 years they've been (half of) the subject of a national emergency; the known dangers to US civil tranquility and the (US) general good, Ndayirukire and Niyombare, are the other half. If you missed it, they were responsible in some sense for unrest in Burundi in 2015. You make "national emergency" and suspension of certain rights permissible for those cases because the law is written so broadly, you own the consequences. Note that a lot of people had no problem with using that law in ways not originally intended.
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