While the bulk of the literature focuses on the vote for parties from different blocs, the purpose of our article is to study the vote for two parties that are ideologically very close to each other: The Social Democrats and the Greens in Switzerland. To that end, we develop a two-step model, where voters first make a selection of parties that are acceptable to them and then make their electoral choice out of this set of acceptable alternatives. We use voting propensities as a measure of the first, consideration step and we show that they strongly depend on the distance between voters and parties on the Left–Right scale. With regard to the second, choice stage of the electoral process we hypothesize about the factors that may account for the varying ability of the two parties to convert potential voters into real voters. Our empirical tests provide encouraging support for our hypotheses regarding the impact of socio-demographic variables and issue voting. Strategic considerations, by contrast, do not seem to matter.