Implied powers. Their authority is spelled out in the constitution -- how it was to be exercised was not. But that's true for all three branches of our government.
When I think of the elder Statesmen in Congress having to administer law in a technological age they are ill equipped to understand, I am worrying about a generational change. A Senator who grew up in the '50s or '60s, for example, who's spent a great deal of his free time getting reelected the last two or three decades is probably not the best equipped guy to determine internet protocol... sadly, he might do just that under the advisement of a clever lobbyist.
Now, just imagine how life was in 1780's America. There is no pfocking way Benjamin, Samuel, John(s), Thomas, Alexander, and George saw this future.
Many tenets are implied powers. Without the room for some evolution in a Republic's lawmaking, a representative government will not long survive.