Background: Elected members of the US Congress rely on staff, including fellows with scientific and engineering expertise, to find and interpret information for use in policymaking. Factors that impede, or facilitate, the communication of scientific information within the institution thus can play a critical role in legislative capacity, but there is a limited understanding of these dynamics in the hyper-partisan body. Aims and objectives: This study presents and tests a four-dimensional model describing how the obstacles to science communication in Congress change depending on whether information is sought for use in support of established policy positions ('strategic use') or to inform decision making ('substantive use'). Methods: Data were collected between November 2017 and February 2019 through interviews with 58 congressional staff members in personal offices assigned to energy, natural resources, and science issue portfolios, and through surveys with 68 science and engineering fellows who completed their year in Congress between 2015 and 2019. Findings: Placing scientists and engineers in Congress as fellows augments staffing and institutional expertise. Yet we find that both staff and fellows experience communication-related impediments in using scientific information. Staff report more challenges in using science to substantively make policy decisions, due not only to lack of time, but also factors such as contacts, access, and information presentation. Fellows report fewer barriers and use science for policy in largely identical ways to staff. Discussion and conclusion: These findings support the proposed model and highlight the importance of staff scientific fluency and the decision-making context for science communication in Congress.