Disinformation represents a danger to the integrity and legitimacy of the electoral process. From our research based on the 2021 Czech parliamentary elections, we introduce a model for measuring the resilience of citizens to disinformation. This model is then used to draw conclusions about the impact of disinformation on their voting behaviour. We argue that it is important to understand this impact in the context of pre-existing beliefs and opinions, and therefore in terms of disinformation reinforcing rather than changing existing views. In particular, we demonstrate how feeling disappointed with one political party can make people more inclined to endorse disinformation that targets it.