be on a razor's edge

To be likely to fail or change drastically very suddenly or at any given moment. The stability of the market is on a razor's edge, as banks struggle to deal with a huge number of failing mortgages and bad debts. The policy norms for the country tend to be on a razor's edge, as the majority in Congress constantly shifts between the two major political parties. She's really on a razor's edge with her reasoning for that project. I would not be surprised if it didn't get funded.