Earlier quoted context omitted.
Does that mean the presidential election's outcome won't make a significant difference for the vast majority of Americans, that whoever is elected - Sanders, Clinton, Trump, et al - will basically administer the Federal government the same way?
I wouldn't say that. The president has a tremendous amount of international influence, and they have control over federal departments and the military to direct a significant amount of their behavior. They just aren't the people that will change campaign finance reform, build walls, or raise the minimum wage. That is kind of what congress does. So you could elect any president and only see legislation they want passe…
Toward the end the study notes: "When the preferences of economic elites and the stands of organized interest groups are controlled for, the preferences of the average American appear to have only a minuscule, near-zero, statistically non-significant impact upon public policy."
At the national level, US democracy is an illusion.