Separation of powers has effectively failed due to the Supreme Court's supreme reliance on precedent, or stare decisis. One bad decision, unless explicitly overturned, has ripple effects on every decision that follows it. Because of SCOTUS' strict adherence to precedent, and their relative unwillingness to overturn bad law except where they absolutely, positively have to, we have a ton of bad precedent on the books, and everybody pussyfoots around them, which leaves more and more resultant bad decisions in their wake.
The second amendment has been as flagrantly violated for years as the fourth is now. "Congress shall make no law" is obscured by endless debate over whether the right belongs to a militia, or whether it is an individual right. After the Heller decision, that debate has shifted over to whether or not a given piece of legislation is "reasonable", as the Heller decision declared legislation must be. This of course ignores the text of the Constitution, that Congress shall make no law, but because they have made laws, and some of those laws have been upheld by bad precedent, we have a circular logic in place. Congress shall make no law, but the last law that was made was upheld, so no laws can be made, so long as they are reasonable. Further, SCOTUS has thus far passed on newer, more updated challenges in the wake of Heller.
They've made the same side-steps on gay marriage. A favorable decision has been reached, but there's no teeth in place to prevent states from re-interpreting the decision however they like, and everything moves so slowly that political parties can reap the rewards from both the passage of a bad law, and its repeal. The democrats passed DOMA, to great acclaim. The democrats claimed success when DOMA was overturned, to great acclaim. The Constitution's purpose is to prevent legislation from catering to the whims of the people, and it is clearly not doing a great job there.
It's hard to imagine that any originalist text or intent would condone today's perennial slaughter of the fourth amendment, but on it goes. People stake their claims on individual words in the clause, while ignoring the text on the whole. This is done on purpose, because there is no penalty for violating the Constitution, and because even if we were to attempt to hold those accountable to the text, it's so easy to say "Well, I read it differently."
The problem is that the Constitution, for as much as we might all love it in theory, is written in plain English, and is subject to interpretation by lawyers. There's a reason lawyerese is used, and it's to prevent plain English readings from being interpretable. But we elect those who are, for better or worse, the most likely to be able to twist its words into meaning whatever we want, and we either can't, or don't hold them accountable for anything above and beyond the next election cycle.
Sorry for the rant.