Sen. Elizabeth Warren (D-Mass.) has been hailed as a progressive hero and, though she's personally panned the idea, a possible lefty alternative to Hillary Clinton in 2016. It stands to reason that an analysis of her voting record would peg her as one of the most liberal members of the Senate, right?

Which is why it's surprising to see that National Journal's annual vote rating — which ranks lawmakers on a liberal to conservative scale — finds her to be the 31st-most liberal senator last year. Warren comes in one spot behind South Dakota's moderate Sen. Tim Johnson (D), who only "evolved" on gay marriage in 2013 and is retiring at the end of this year.

So what gives? Is Warren more media-made myth than substance?

Spoiler: Nope.

To the methodology!

There's one big problem with the ranking system. While it does a nice job overall of defining votes as either "liberal" or "conservative," the rubric is nonetheless reductive. It works, in short, by checking how often a lawmaker voted with the majority of her caucus, and how liberal or conservative those votes were. For the most part this means that the more often a Democrat voted with Democrats, the more liberal she would be. (You can read the full methodology here.)

While we do have a two-party system, classifying votes under a binary system strips away their context. An explainer on how the rankings are calculated concedes that point:

Keep in mind that no single measure of voting behavior is likely to be perfect. For instance, consider the hypothetical example of a vote in the House on cutting domestic spending. Let's say the bill passed with overwhelming support from House Republicans and overwhelming opposition from House Democrats. A vote for the bill would be counted as conservative and a vote against the bill would be counted as liberal. But let's say a handful of House Republican conservatives voted against the bill on the grounds that the budget cuts didn't go far enough. In so doing, they voted against most conservatives and with most liberals. Their votes would be counted as liberal because they voted with liberals. It's beyond the capacity of a vote-ratings system to determine why a member voted the way he or she did on any particular piece of legislation. [National Journal]

Though some of those votes didn't make the cut specifically for that reason, others did. And that seems to be what's at play here.

Take a proposed amendment to the National Defense Authorization Act, sponsored by Sen. Carl Levin (D-Mich.), on the transfer or release of some Guantanamo detainees. Only four Democrats, including Warren, voted against the provision. The rankings give a "no" vote there the most conservative possible weighting.

Warren was joined in voting against the amendment by Democratic Sens. Mark Pryor (Ark.), Patrick Leahy (Vt.), and Ron Wyden (Ore.), as well as Independent Sen. Bernie Sanders (Vt.). Pryor likely voted "no" since he's up for re-election in a light red state. But Leahy, Wyden, and Sanders are all some of the most liberal members of the Senate; Sanders is a self-described Democratic socialist.

Those votes were most likely protests against closing Guantanamo piecemeal. Days before the vote, Leahy called for completely closing Guantanamo, period. Even the White House, which supported the measure, preferred that it be stronger.

Still, since those votes appear on paper as breaks from the party, they serve as signals of conservatism in National Journal's rankings. So though those senators all scored as liberals on economic issues, they graded out as centrists on foreign policy. As a result, Leahy (25th), Wyden (34th), and Sanders (37th) all fell closer to the middle of the list along with Warren.

On another level, the vote ranking does only that: rank votes. Warren's liberal cred comes mostly from coming up with the Consumer Financial Protection Bureau (CFPB) before taking office. And since coming to Washington, she's advocated expanding Social Security, and talked (semi-seriously) of raising the minimum wage to $22, positions few elected Democrats are progressive enough to embrace.

Now, Warren did vote to repeal a medical device tax in ObamaCare, which put her at odds with most in her party. And there are some legitimate signs that she may not be quite as progressive as advertised.

But make no mistake: Warren is no moderate. She's a liberal unafraid to break with the party when she feels it isn't being liberal enough.