In a paper presented last week at a conference in Chicago, two political scientists compared Republican senators’ voting records to their perceived levels of conservatism among grassroots activists. (You can read a detailed description of the paper’s methodology here, but it’s worth noting that the surveys were conducted throughout the 2016 election.) What they found was that some of the senators with the most traditionally conservative voting records—like Arizona’s Jeff Flake, and Nebraska’s Ben Sasse—were viewed among activists as fairly moderate. Meanwhile, former Alabama Senator Jeff Sessions—whose record is considerably more moderate than many of his peers’—was viewed as one of the chamber’s most conservative lawmakers.

The explanation for these discrepancies?

The paper’s authors—Daniel Hopkins, from the University of Pennsylvania, and Hans Noel, from Georgetown— have a theory: Sasse and Flake were both outspoken Trump critics during the election, whereas Sessions was one of the president’s earliest and most vocal cheerleaders.