Explanation
The claim is not conclusively established. Plutocracy means rule by the wealthy. Research provides evidence of unequal political influence in the United States, but turning those findings into a definitive classification of the whole country requires an explicit standard for what counts as rule by wealth.
A 2014 study by Martin Gilens and Benjamin Page examined 1,779 policy issues and found substantial independent influence for economic elites and business-oriented interest groups, with little or no independent influence for average citizens in their model. These findings support concerns about economic-elite domination, but do not by themselves establish a comprehensive classification of the United States today.
The interpretation is also contested. Omar Bashir challenged the statistical inferences in 2015, and Gilens disputed that critique in 2016. These publications debate the interpretation of historical policy data; they are not independent contemporary measurements of the entire political system. The evidence supports taking unequal influence seriously without presenting plutocracy as a settled factual label.
Key takeaway
Evidence of wealthy Americans' disproportionate influence does not conclusively establish that the United States is a plutocracy.