To win democratic elections that are not fully subsidized by the government, nonwealthy candidates must be supported by wealthy patrons. This makes plausible the belief that these candidates will compromise their views to win that support. But since the wealthy are dispersed among the various political parties in roughly equal proportion to their percentage in the overall population, this belief is false.
The argument is vulnerable to criticism on the grounds that it fails to consider that in democracies in which elections are not fully subsidized by the government, positions endorsed by political parties might be much less varied than the positions taken by candidates.