Campaign donors and corporate interests have greater access to Congress, and the legislative agenda and policy outcomes reflect their preferences. How this privileged access converts into influence remains unclear because petitioner-legislator interactions are unobserved. In this article, we report the results of an original survey experiment of 436 congressional staffers. The vignette manipulates a petitioner’s identity, the substance of the request, and the supporting evidence being offered. We test how likely staff are to take a meeting, to use the information being offered, and to recommend taking a position consistent with the request, as well as whether they perceive the request to be congruent with constituent preferences. Donors and lobbyists are no more likely to be granted access than constituents, but staffers are more likely to use information and to make legislative action recommendations when the information source is an ideologically aligned think tank. Subgroup analysis suggests these effects are particularly strong among ideological extremists and strong partisans. And, information offered by aligned think tanks are thought to be representative of constituent opinion. Our results reveal the partisan and ideological predispositions that motivate legislative action that is more costly than merely granting access.