One frequently heard refrain around the liberal blogosphere is “[fill in the blank with name of Democratic congressperson who voted the wrong way on the important legislation of the day] is a bad Democrat; let’s primary him!” That’s certainly a healthy instinct, as credible primary challenges have occasionally yielded good results, either with a victory for a more progressive person or with a loss but with the winner chastened and moved to the left. But it’s often delivered without much thought about the nature of that person’s state or district, and what kind of candidate that place might actually support. Most of us have a basic understanding that liberal places tend to elect liberals, conservative places tend to elect conservatives, and swingy places can’t make up their minds but tend to elect moderates of both parties … but how do we refine that knowledge into something useful?

In addition, around this time every year, there’s a flurry of discussion of who’s the “most liberal” or “most conservative” members of Congress, which usually coincides with National Journal’s release of its congressional rankings. Now, by itself, that’s not very interesting, not just because the methods for distilling everything that a congressperson says and does into a number are very subjective, but also because such lists mostly just contain the same usual suspects, found in non-competitive states or districts, year after year.

But they do provide a helpful tool; by combining them with information about how their state or district has voted in recent years, we can analyze whether a congressperson is performing in line with how you’d expect him or her to, given their constituents. In other words, how “valuable” are they, or how good a “fit” are they, given the kind of district they have to work with?

Most congresspersons, in fact, do perform about how you’d expect, but it’s the ones who don’t who are the interesting ones and deserving more of our attention. We can use this method to spot Democrats who are underperforming their districts and might benefit from a primary challenge to straighten up or get out; we can also use it as a means of finding below-the-radar Democrats who are voting more liberally than their districts would warrant, and giving them some encouragement. It can also help us spot potentially vulnerable Republicans, the wingnuts hidden in swing districts whose records provide ample ammunition for a general election attack.

That’s a project I’ve attempted several times in recent years; those of you who were longtime readers of Swing State Project probably remember the PVI/Voting Index (named that because it plots a district’s lean, “PVI” according to the Cook Political Report, against a congressperson’s voting record) as a staple at that blog. With another year’s worth of aggregators releasing their congressional voting data, let’s take another look at the Index.

It’s deceptively simple. Rank every state from 1 to 50 or every congressional district from 1 to 435 in terms of how Democratic its presidential voting record was in the last two elections. Rank every senator from 1 to 100 or representative from 1 to 435 in terms of how liberal his or her voting record was, and then calculate the difference. A larger difference, depending on the direction, is an indication that a person is overperforming or underperforming his or her district’s lean. (There are a lot of methodological issues that go along with this assumption, which I’ll discuss over the fold; first, though, let’s get right to the numbers.)

We’ll start with Senate numbers, starting with Democrats who are underperforming their states. For short, we’ll call them “bad Dems,” though many of them aren’t especially bad, but have records that put them toward the middle of the Democratic caucus while coming from solidly blue states. A couple of them are actually more objectionable, to the extent that they’re centrists near the midpoint of the whole Senate, while still from blue states (that basically boils down to Joe Lieberman, who we’ll be rid of next year anyway, and Tom Carper).

First things first: You’re probably wondering what all these abbrevations and numbers mean. “DW/N,” “NJ” and “PP” are the names of the three aggregators that I’m using: DW/Nominate scores, National Journal scores, and Progressive Punch scores. There are other aggregators that I’m not using, and there are quirks to each of these three aggregators that encourage me to use each of their scores separately (rather than averaging out their scores, which forces too much apples-to-oranges comparison). I’ll talk about the aggregators a little more over the fold, in the context of methodology.

And here’s how the score is calculated. Let’s use the example of Carper, who’s the most underperforming Democrat according to DW/Nominate scores. He’s in Delaware, which has a PVI of D+7.0, making it the 10th most liberal state. However, because each state has two senators, that means that each of the two senators from Delaware are tied as having the 19.5th most liberal constituency. Carper has a DW/Nominate score of -0.189, which makes him the 50th most liberal senator (meaning the only Democrats trailing him are Claire McCaskill, Joe Manchin and Ben Nelson, each of whom has a much tougher state to work with). Find the difference between the PVI ranking (19.5) and the Vote ranking (50), and, voila, you come up with a PVI/Vote Index score of -30.5.

I’m a firm believer in showing all your work, but I don’t want to numb your minds with graphs showing that kind of calculation for everyone in Congress. However, if you do want to see that, here is a link to the Google Doc spreadsheet that does have those calculations for everyone, if you’re curious what a particular person’s score is (or how their votes or their district stacks up by itself).

And now let’s look at the Democrats who are most overperforming their states. We’ll call them the “good Dems” though most of them on this list haven’t always been netroots favorites; they’re on the list by virtue of providing moderate/centrist records in dark-red states that would otherwise elect Republicans. For instance, Kent Conrad is one of the caucus’s main budget hawks, while Ben Nelson is … well, what hasn’t Ben Nelson done to tick us off? On the other hand, Sherrod Brown makes the list by being in the Senate’s most-progressive echelon while representing a swing state.

Here are the Republicans who are most overperforming the lean of their states, hence the ones with the ugliest records: either quasi-moderates in blue states (Scott Brown, Mark Kirk), or else the hardest of the hardcore conservatives in swing states (Pat Toomey, Kelly Ayotte). Unlike the Democrats, we’ve actually got some unanimity among the various aggregators as to who’s the most out-of-step with his state of all: Wisconsin’s Ron Johnson. Unfortunately, with the exception of Brown, all of these senators are freshmen elected in 2010, so we’re stuck with them for four more years … though, given the way they’ve voted in relation to their states’ general leans, November 2016 ought to be quite the day of reckoning.

Finally, here are the underperforming Republicans, who put up voting records less conservative than would be expected from their dark-red states. I’m listing them really for the sake of curiosity and/or symmetry. Unlike the overperforming GOPers, we aren’t going to make targets out of them in a general election (unless an opportunity for mischief presents itself, like Alaska in 2010); we can only sit back and enjoy some popcorn while the Club for Growth, FreedomWorks and their ilk attempt to primary them from the right.

We’ll look at the House, and answer some methodological questions, over the fold …

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