Lawful interception is precisely not made for "three letter agencies", since the latter derive the majority of their power from not spying on the law subjects of their own country. Although the US have of course intentionally muddled this with FISC and at times outright disregard for that simple principle.

The US really needs a distinction between executive powers (which exist because legislative bodies grant the executive branch wide latitude), and legislative powers (specific things the legislature has said to do).