Sen. Elizabeth Warren (D-MA) addresses the Rev. Al Sharpton's National Action Network during a post-midterm election meeting in the Kennedy Caucus Room at the Russell Senate Office Building on Capitol Hill November 13, 2018 in Washington, DC. (Chip Somodevilla/Getty Images)
CNN's Enten: Warren is a below-par candidate
02:25 - Source: CNN
CNN  — 

Now that the race for the 2020 Democratic nomination has officially started, one of the big issues that will likely come up is which candidate is the most electable.

One way to find that out is to see how the different possible candidates have done in the past. Of course, it’s difficult to compare candidates when they run for different offices in different years.

There are, however, six potential 2020 Democratic contenders ran who ran for the US Senate in 2018.

The big takeaway from those results: Sens. Amy Klobuchar of Minnesota and Sherrod Brown of Ohio are above-average candidates on the question of electability, while Sen. Elizabeth Warren of Massachusetts – who announced Monday that she’s formed a committee to explore a 2020 presidential run – is below average.

To come to that conclusion, I followed a pretty simple formula. I looked at how Brown, Klobuchar, Warren, Sen. Kirsten Gillibrand of New York, Texas’ Beto O’Rourke and Sen. Bernie Sanders of Vermont did in their 2018 Senate races. Then I examined how Democratic US House candidates in those same states performed. Thanks to Catalist, a data company that works with Democrats and others, we can calculate how unopposed House candidates would have done in races had they had opponents.

Klobuchar won her race by 24 points. Democratic House candidates in Minnesota won by 11 points, which is the same margin Klobuchar’s home state colleague, Democratic Sen. Tina Smith, won her special election by. So Klobuchar had a 13-point overperformance.

Klobuchar’s win is particularly impressive when you look at all Democratic Senate candidates running in 2018. Only Sens. Heidi Heitkamp of North Dakota and Joe Manchin of West Virginia did better than Klobuchar compared with the US House candidates in their states.

Now, you might think Klobuchar, Heitkamp and Manchin were able to do so relatively well because they don’t have particularly liberal voting records. That may be the case, though Brown’s Ohio performance suggests well-known progressives can also score well.

Brown won his Ohio race by 7 points. That may not seem like a lot, but Ohio Democrats struggled in House races. All told, Republican House candidates in Ohio beat Democratic House candidates by 5 points. In other words, Brown did 12 points better than the baseline.

Brown can rightfully claim that he flipped a red-leaning state blue in the midterms. That’s a fairly powerful message given that Hillary Clinton would ha