The last session of the House of Representatives, from 2011 to 2012, was the most conservative in more than 60 years, according to the Brookings Institution.
The think tank, along with the American Enterprise Institute, released a trove of data last week—the annual update to the Vital Statistics on Congress—and the data show a stunning shift to the right among House Republicans over the past 35 years. House Republicans have been getting more conservative than House Democrats have been getting liberal, according to the data.
The rankings are based on ideological scores assigned to lawmakers' voting records by professors Keith Poole of the University of California (San Diego) and Howard Rosenthal of Princeton University.
House Democrats have been slow to veer leftward, with Southern Democrats becoming liberal faster than their non-Southern counterparts.
The Senate, meanwhile, hasn't exhibited the same sharp rightward shift, with the entire chamber hovering around the center of the ideological spectrum over the last 65 years.