In this article, we use a structural equation model (latent variable mediator analysis) to show that a strong local base has two key effects on Liberal Democrat support in the 2010 general election. First, it has a direct effect on Liberal Democrat support at Westminster elections by bridging the electoral 'credibility gap'. Second, local success has a significant indirect effect on party performance through campaign effort. Here we find that the Liberal Democrats obtain appreciable electoral benefits where they campaign intensely. They also use grassroots campaigning to recruit local activists and party workers, which cements the local party infrastructure and enables the party to be more effective in targeting local resources. The total standardised effect is therefore fairly substantial even after controlling for an array of other predictors. It is also larger than the total effect of local election success on both Conservative and Labour Party support in 2010. Far from being inconsequential, winning seats at the local level provides a significant boost to the Liberal Democrats' performance in general elections.