Scientific expertise plays an increasingly central role in policymaking, yet growing distrust toward science among Americans raise questions about how Congress engages with expert witnesses. Drawing on a comprehensive dataset of 760,000 congressional witnesses from 1961 to 2022 and committee hearing transcripts from 1997 to 2018, we identify those affiliated with universities and think tanks and analyze legislators' interactions with them. Using the two measures of legislators’ questioning styles---grandstanding and analytical engagement---we assess how issue polarization, partisanship, and constituency characteristics shape congressional treatment of expertise. We find that both parties engage in more grandstanding when questioning research witnesses, particularly those from think tanks and during hearings on polarized issues. Republicans consistently exhibit higher grandstanding and lower analytical engagement, especially toward university-affiliated scholars. Members representing constituents with lower education attainment tend to grandstand more toward researchers. These patterns raise concerns about democratic accountability and effective functioning of U.S. Congress.