What do you think was the "point of no return" for the Ming dynasty?

[Mort the Reaper]

There are many who believe that, with the benefit of hindsight, we can tell when a nation's fall became inevitable. But there's almost always debate on exactly when things became bad enough that recovery was impossible. I've heard a lot of debates about this when it comes to a whole number of different empires, and the various dynasties of China are no exception. The Ming dynasty seems to be especially contentious in this regard, at least judging from personal experience.

So I thought I'd ask you guys: what do you think the "tipping point" was for the Fall of the Ming dynasty? When do you think its end was only a matter of time?