Based on the results of the March 2006 Senatorial races, this article assesses the 2003 political reform in Colombia by considering its central features: electoral threshold, d’Hondt formula, limitation of one list per party, and optional open lists. Our analysis shows that the reform satisfies its most basic goal of promoting party cohesion in the electoral dimension. The article also includes an analysis of the factors that, given the new set of rules, affect the likelihoods of electoral success for senatorial candidates. In the conclusion, the article discusses how the political reform, by design, can only have an impact on the electoral behavior of the parties. It also argues that it is necessary to modify the legislative behavior of the parties and the structure of campaign financing in order to produce parties
that are effectively cohesive and disciplined.