  Voting is a simple mechanism to aggregate the preferences of agents. Many
voting rules have been shown to be NP-hard to manipulate. However, a number of
recent theoretical results suggest that this complexity may only be in the
worst-case since manipulation is often easy in practice. In this paper, we show
that empirical studies are useful in improving our understanding of this issue.
We demonstrate that there is a smooth transition in the probability that a
coalition can elect a desired candidate using the veto rule as the size of the
manipulating coalition increases. We show that a rescaled probability curve
displays a simple and universal form independent of the size of the problem. We
argue that manipulation of the veto rule is asymptotically easy for many
independent and identically distributed votes even when the coalition of
manipulators is critical in size. Based on this argument, we identify a
situation in which manipulation is computationally hard. This is when votes are
highly correlated and the election is "hung". We show, however, that even a
single uncorrelated voter is enough to make manipulation easy again.
