The Trump campaign has launched an attack against Sen. Kamala D. Harris (D-Calif.) that doesn’t quite ring true to most ears, but is also technically backed up by data: In 2019, she was ranked the most liberal U.S. senator. That’s according to the nonpartisan, independent congressional tracker GovTrack.us.

It’s an attack President Trump has latched onto as Republicans try to find something to stick Harris with. Here he is Thursday morning with Fox Business Network talking about Joe Biden’s vice-presidential pick: “Well, she’s radical left, now she tries to pretend she’s not, but she is the most liberal person in the U.S. Senate, acknowledged to be.”

But wait, how can something be true according to the data but also not feel right? Could Harris really be more liberal than Sens. Bernie Sanders (I-Vt.) or Elizabeth Warren (D-Mass.)?

The answer is that the data GovTrack.us tracks, while useful, is not a complete look at how liberal or conservative a politician is or would govern. “We always say that one number can never represent the complete picture of a politician,” said Joshua Tauberer, founder and president of GovTrack.us.

Politicians are more than the legislation they co-sponsor or even vote on. The positions they take outside the halls of Congress also reflect how they would make decisions. And while Harris has tendencies that lean left, she doesn’t seem to always act on them.

To get their rankings that found Harris the most liberal senator in 2019, GovTrack.us tracked bills sponsored and co-sponsored by each lawmaker. How often were those bills with the other side? The most centrist Senate Democrat in 2019 was Sen. Kyrsten Sinema (D-Ariz.). Last year, 59 percent of the bills she co-sponsored were written by a Republican. Compare that to Harris, where 15 percent of the bills she co-sponsored were written by Republicans.

One of the most prominent bills Harris signed onto was also arguably one of the Senate’s most liberal proposals, Sanders’s Medicare-for-all legislation.

So by the picture of legislation she signed her name onto in Congress during this period, yes, Harris was pretty liberal in 2019.

But this is also just one year. And it was the year Harris was running for the Democratic presidential nomination, so she had an incentive to co-sponsor liberal bills, since primaries tend to push candidates to the extremes of their party.

If you look at a five-year span provided by GovTrack.us — although Harris was not in the Senate all of those years — she’s still among the most liberal senators by this marker. But Sanders and a few others are more so.

Here’s the big “but” to the “most liberal” tag the Trump team is using against Harris. Co-sponsoring legislation is just one way to measure a lawmaker’s ideology. And while GovTrack.us has found that it matches up pretty well with a politician’s general ideology, it’s also one of the most under-the-radar ways a lawmaker can take a position. Politicians come up with their own proposals that can differ with the legislation they sign onto in Congress. In Harris’s case, some of her proposals differ in big ways from bills she sponsored or co-sponsored.

Here’s an example. Even though Harris signed onto Sanders’s Medicare-for-all bill, she came up with her own health-care plan during the presidential primary that was decidedly not a full, single-payer health-care system. She proposed allowing private insurers to continue to provide similar insurance as Medicare. It was more similar to centrist primary candidate positions such as those of Pete Buttigieg, that people should get Medicare if they want it but not be forced into it.

Back in Congress, she also supported (as did all Senate Democrats) a 2018 criminal justice reform bill that Trump signed into law. You could argue that giving the president one of his major legislative achievements isn’t an extreme liberal thing to do.

Tauberer notes that during Democrats’ recent intraparty debate on whether to get rid of the Immigration and Customs Enforcement agency, Harris was critical of ICE, saying she thought it needed a total restructuring. But she made it clear that she never supported abolishing it like other lawmakers on the liberal spectrum did.

The point is, there are a number of ways to look at a politician’s ideology. When you look at Harris more holistically than the legislation she’s co-sponsored, it doesn’t make sense to call her the most liberal senator.

“All these data points don’t add up to just a simple picture of Harris being extremely liberal,” Tauberer said.

Harris actually was criticized for her varied positions during her presidential campaign. Some voters and supporters were confused about what she was for. She was kinda supporting Medicare-for-all but also kinda not. Biden’s campaign said at the time that Harris’s health-care plan represented a “new, have-it-every-which-way approach.”

Now that they’re on the same presidential ticket, Biden and Harris are probably going to be on the same page about policy. That could bring Harris even further to the center of her party, in a way that tracking her legislation in Congress wouldn’t reflect.