When we use historical methods and sources we're doing history. When we use influence and governance, we're doing politics. The distinction between history and politics isn't in the event, it is in your relationship to the event and the use to which you're trying to put the event.
If I research the legal status of Kosovo with an intent to determine how a fully independent Kosovo will affect my country, I'm doing politics. If I research the legal status of Kosovo with an intent of understanding the effect of the status of Kosovo on the evolving definition of a nation-state, then I'm probably doing history.
If I research WWII with the intent of understanding how the Clivedon set incorporated fiscal conservatism with secular chauvinism, I'm probably doing history. If on the other hand I research the Clivedon set with the intent of understanding the fundamental hypocrisy of secular chauvinism and fiscal conservatism, and the specific intent of understanding how that hypocrisy can be manipulated, I'm probably doing politics.
Update: An even better example just occurred to me - A close friend of mine is studying the adoption of the US constitution to determine whether secession is legal; if it is legal, then it supports certain conclusions about states rights, and the role of the Federal government. I'm discussing it with him because I'm interested in how the states came together to form a union, and how that concept of union evolved over time. From your perspective, the Constitution is history - a done deal. From his perspective, it is an element in a political discussion. From my perspective it is a fascinating era in history.
Contrary to your assertion, no historical event is ever "ended" - they all have implications for the current day. That's what Santayana means when he says that those who cannot remember the past are condemned to repeat it.