In 2023, the Robert Wood Johnson Foundation worked with ORS Impact to conduct an evaluation to understand progress during the 117th Congress on three federal policies: the Advance Premium Tax Credit (APTC), the Child Tax Credit (CTC), and closing the Medicaid coverage gap. This brief summarizes what we did and what we learned about: (1) collecting and analyzing data, (2) developing and testing hypotheses, and (3) reporting to conduct process tracing on the three policies. The primary audience for this brief is the evaluation field, particularly evaluators considering applying process tracing to a policy advocacy evaluation. Our hope is that sharing our approach and lessons learned can make it easier for others to implement this method with high quality for other advocacy and policy change evaluations.