Congressional enforcement of federal guarantees of the rights of life, liberty and property, per Section 1 of the 14th Amendment, by authority of Section 5: "The Congress shall have power to enforce, by appropriate legislation, the provisions of this article."
One should say, "attempted" enforcement, since the effort was nullified by the judicial branch and had no effect whatsoever on the case. Congress indisputably had the constitutional authority to act, so that's not an issue. Nothing actually came of it, so that's not an issue either. But shame on the judiciary for butting in, and more shame on the judiciary for taking away an innocent citizen's basic rights!
This 1865 lithograph, accompanying an article on the 14th Amendment (ratified in 1868), conveys that freed slaves were now U.S. citizens with all the rights and privileges of citizenship, and that no state could lawfully deprive any individual of life, liberty and property.
If you wish to call it "intervention," that doesn't change the fact that it did not delay the court-ordered death of an American citizen by one minute. "Intervention" is the wrong word because it is meant to deceive. It hides the history of the litigation and leaves the false impression that the feds were gratuitously butting into a private matter. But it wasn't a private matter and Michael Schiavo himself initiated government intervention in 1998 -- seven years earlier!
Law School dean Gary Amos was so outraged by judicial misbehavior throughout the case that he stated that, apart from two or three dissents, every single judge involved including all nine sitting members of the Supreme Court, "must" be impeached.
Prof. Amos's essay is linked at #199 above. See also this forcefully argued dissent by Judge Wilson in the 11th Circuit: Judge Wilson's "strong" dissent (see pages 11 through 21)