How a Political Clique can control a vote
There is also another way in which one man (well strictly it is two people) could control the Senate - by the judicious use of political cliques, defined as a subgroups of deputies. If a political clique is formed such that it contains more than 50% of the deputies in the Senate and each member of this clique agrees that:
The clique will conduct a secret vote on each issue among its members
Each member vote as a block, bound by the vote of the clique when the issue comes up in the Senate
It is thus clear that the remaining deputies who are not members of the clique will have no say when the issue comes up in the Senate as the issue will be predecided.
Sub-Cliques
Although a clique can control a vote in this way it is clear that the clique can itself be controlled by sub-cliques. Any sub-clique whose members account for more than 50% of its parent clique can control the parent clique and hence the vote in the Senate, at long as its members abide by the same rules.
Recursion
It can thus be seen that any clique can be recursively broken down into progressively smaller cliques which can control the overall vote. Eventually a point is reached where a clique of two people controls the entire Senate. It is obvious that this clique cannot be broken down into smaller cliques which could control it. It is at this point that the vote of one man controls the Senate.
Imagine that in this smallest clique of two people they take it turns to write down their vote on a piece of paper and place it face down on a table. The second person to vote now controls the Senate as if he votes the same way as his companion then the inexorable chain of cliques will result in the Senate following his lead.