President Trump’s reelection team must have been ecstatic to discover, buried in a wonky government-tracking website, a bit of data that helped it make the case it has wanted to make for months — that former vice president Joe Biden is beholden to the far-left wing of his party. Why, according to GovTrack, his pick to serve as running mate, Sen. Kamala D. Harris, is the most liberal member of the Senate!

In an interview on Fox Business on Wednesday, Trump was asked about the selection of the California Democrat.

“Well, she’s radical left,” he replied. “Now she tries to pretend she’s not, but she is the most liberal person in the U.S. Senate, acknowledged to be.”

One can certainly dispute the extent to which being a member of the Senate overlaps with participation in any radical movements, but Trump is not wrong about GovTrack’s determination. The site evaluated all 100 senators, and Harris emerged as the most liberal.

But … what does this mean? What’s being evaluated? How? When?

GovTrack’s website explains what it measures:

“The data that goes into this analysis is a list of who sponsored or co-sponsored which bills. The process doesn’t look at the content of the bills or the party affiliation or anything else about the Members of Congress, but it is able to infer underlying behavioral patterns, some of which correspond to real-world concepts like left-right ideology.”

“The left-right score reflects the dominant ideological difference or differences among Members of Congress, which changes over time,” the site notes. And, in fact, looking at the past three years of ratings (since Harris joined the Senate in 2017), shows some of that movement.

In 2017, Harris was the eighth-most-liberal senator. In 2018, fourth. As she prepared a 2020 presidential run, she became the most liberal — joining Sens. Bernie Sanders (I-Vt.), Cory Booker (D-N.J.) and Kirsten Gillibrand (D-N.Y.), all of whom also ran. Politics appears to play a role in another way, too: Sen. Doug Jones (D-Ala.), up for reelection in a deep red state this year, became more conservative.

This suggests that the rating system is capturing something significant. But that Harris isn’t generally seen as one of the most liberal members of the Senate suggests that it’s also potentially missing something, which GovTrack’s Josh Tauberer readily acknowledges.

“Obviously our analysis is at odds with what other serious analysis of Harris’s career has found, and I think the short answer is that both things can be true: She can both be sponsoring/co-sponsoring left-leaning legislation, something with typically little risk, while also being pragmatic when push comes to shove on risky and impactful decisions, as evidenced by her career as a [San Francisco district attorney] and [California attorney general],” he said in an email. “You could also see this in how she responded to the Abolish ICE movement — by not joining it. Another example might be Harris’s vote in favor of the FIRST Step Act, the criminal justice reform bill that President Trump counts as one of his achievements, something Harris could have voted against as not progressive enough, but she didn’t, she supported it (as did all Democrats, though).”

Tauberer added that she often introduces bills that focus on traditional Democratic issues but approach solutions in atypical ways for a liberal.

And it could be politics.

“Our analysis might also reflect a possible (but unsubstantiated) deliberate attempt by Harris to co-sponsor legislation to pull her record left ahead of the primaries,” he added, “or, conversely, that other senators could have been unwilling to work with Harris in order to hurt her campaign.”

GovTrack also takes a broader view of how senators vote, compiling a five-year analysis of how members of the body participate in crafting and pushing legislation. In addition to ideology, GovTrack looks at leadership, measuring, among other things, the frequency with which senators are joined in their proposed legislation by other senators.

When we overlap those measures and look at the broader time frame, Harris stands out to a lesser degree. Over the course of her time in the Senate, she’s still one of the most liberal members but is among several others.

Even with that additional level of analysis, Tauberer points out that the analysis is necessarily rudimentary.

“Our analysis, and political analysis, generally talks in terms of the one-dimensional left-right axis,” he wrote. “But of course people have more complex views than can be distilled into one number, and the question then is what does our numerical analysis in particular do when someone’s views don’t fit into the model?”

That’s not something that’s trivial to answer. (If it were, it would be modeled.) But we can look at other indexes of partisanship to get a broader sense of how Harris is viewed.

Voteview, for example, is a project of the political science department at the University of California at Los Angeles. It tracks members of Congress on two dimensions. The first is ideology, as assessed by considering votes centered on the extent of support for government intervention and deployment. The second is a bit more esoteric, measuring, in essence, the extent to which a member of Congress has expressed a willingness to buck the establishment.

On this measure, too, Harris is among the most liberal senators, surpassed only by Sen. Elizabeth Warren (D-Mass.).

But you can also see the limits of the methodology Tauberer hinted at: Would one generally consider Sanders the fourth-most-liberal member of the chamber?

Or, if we add in members of the House, is Harris more liberal than Rep. Alexandria Ocasio-Cortez (D-N.Y.)?

Part of this is certainly a function of Ocasio-Cortez’s relatively limited record, given her having joined Congress last year. But part of it, too, is a limitation of the measurement.

That these indexes generally do capture the divides that exist in Congress suggests an obvious value to them. Harris’s record is farther left than most or all of the other senators and, apparently, increasingly so in recent years. Whether that necessarily correlates to her being the most liberal senator in some Platonic sense is unresolved.

Save for the president’s reelection bid, of course.