  Influence among individuals is at the core of collective social phenomena
such as the dissemination of ideas, beliefs or behaviors, social learning and
the diffusion of innovations. Different mechanisms have been proposed to
implement inter-agent influence in social models from the voter model, to
majority rules, to the Granoveter model. Here we advance in this direction by
confronting the recently introduced Social Influence and Recurrent Mobility
(SIRM) model, that reproduces generic features of vote-shares at different
geographical levels, with data in the US presidential elections. Our approach
incorporates spatial and population diversity as inputs for the opinion
dynamics while individuals' mobility provides a proxy for social context, and
peer imitation accounts for social influence. The model captures the observed
stationary background fluctuations in the vote-shares across counties. We study
the so-called political strongholds, i.e., locations where the votes-shares for
a party are systematically higher than average. A quantitative definition of a
stronghold by means of persistence in time of fluctuations in the voting
spatial distribution is introduced, and results from the US Presidential
Elections during the period 1980-2012 are analyzed within this framework. We
compare electoral results with simulations obtained with the SIRM model finding
a good agreement both in terms of the number and the location of strongholds.
The strongholds duration is also systematically characterized in the SIRM
model. The results compare well with the electoral results data revealing an
exponential decay in the persistence of the strongholds with time.
