The Senate’s static diversity also bucks a trend in the federal government under President Obama, who has appointed a record percentage of minorities and women to posts requiring confirmation. The Senate, therefore, is approving a lot of minorities; it just isn’t hiring them. Jones told me that his research indicated that staff diversity in the top rungs of the Senate hadn’t changed much since the 1980s, despite periodic efforts to highlight and remedy the problem. In the mid-2000s, then-Senate Majority Leader Harry Reid created a diversity initiative to encourage minority hiring by Democratic offices. But Jones said the impact of that effort had been mixed: It helped staffers of color get their foot in the door with entry-level positions, but it didn’t make much difference in senior-level jobs. “Senior positions are more competitive, they’re more political, and the opportunities to fill these vacancies are more rare,” Jones said.

The study limited its focus to the top positions in personal and committee Senate offices based in Washington, noting that some senators had hired minority staffers in their home states and that there were some senior-level staffers of color in the separate party leadership offices. The House has a considerably more diverse staff at all levels, reflecting a more diverse elected membership. Around 70 of the chamber’s 435 lawmakers are members of either the Congressional Black Caucus or the Congressional Hispanic Caucus.

The Senate does not keep demographic data on its workforce, and so Jones had to rely on public records and interviews to conduct his study. One of the recommendations in the report is that the Senate begin to track and analyze data about its staff—something Congress requires of most federal agencies, but not of itself. The report also urged the Senate to adopt a version of the NFL’s “Rooney rule,” in which teams are required to interview at least one minority candidate for each top-level vacancy, even if they ultimately don’t hire them. One reason for taking the NFL’s lead is that the Senate is actually quite similar in structure: a weak central administration and dozens of independently-run teams, or offices. “While a Rooney rule alone is insufficient because many Senate offices will continue to hire within their personal staffs, the Rooney rule gives candidates of color experience interviewing and focusing on qualities to be a key Senate staffer,” Jones wrote. “Use of the Rooney rule may also increase the number of mid-level staffers of color, and thus the pool of candidates for top staff positions.”

Will that happen anytime soon? That seems unlikely. A spokesman for Senate Majority Leader Mitch McConnell wouldn’t comment on the study, and neither party has made staff diversity a priority since Reid launched the Democratic effort nearly a decade ago. After the report was released on Tuesday, Reid issued a statement saying it “serves as an important reminder of how much work we still need to do.”