light the (or a) fuse (or touchpaper) do something that creates a tense or exciting situation.

☞ The image here is of lighting a fuse attached to gunpowder, fireworks, etc. in order to cause an explosion. A touchpaper, which is used in the same way as a fuse, is a twist of paper impregnated with saltpetre to make it burn slowly.

2012Real Clear Markets As long as this mentality remains in Europe, yesterday's protests won't be the only source of instability in Europe's financial future: the [European Central Bank] itself could light the fuse.