There are two separate issues covered in Thomas Edsall's Thursday, March 30, 2018 article in the New York Times. First, exit polls have problems with race and education. Certainty true, but not exactly as the author describes. Second, Democrats have problems messaging race and education. Certainty true, but not exactly as the author describes.
Data: while white-working class voters are a higher percentage of the Democratic electorate than reported in the exit polls: we already knew that on Election night and it is probably not as dramatic as Pew notes.
1) Exit Polls Under-estimate Non-college graduates: As the author notes, very deep in the article, it is common knowledge among pollsters and political scientists that the exit polls have a lot of problems. Exit polls are polls that are constrained by needing to be on the ground on Election Day (because the networks want to report that) and mix with polling for early voters. They do not benefit from the hindsight of the voter files that have race and education matched with who voted. Thus, they under-estimate non-college graduates.
2) Pew is a Poll Too: Pew is a poll-of-polls, but it is still a poll. The author should have made this clear, as it was odd how much space he used to bash exit polls, but then just blindly called Pew right and moved onto the data.
3) Pew is closer to correct: non-college educated voters, even white non-college educated, are a sizable portion of the Democratic voters.
4) Pew may over-estimate white voters: since Pew is a poll-of-polls it is not easy for me to delve into the methods. But, the voter files which provide the "ground-truth" of who voted (but, not for whom) have issues with both race and education. Voter files are built county-by-county and contain actual: age, gender, and address. They may contain race in a few states. But, mostly race and education is imputed or matched from other data. Target Smart provides a very nice probability of each race for every person. But, frequently researches rely on the best-estimate for race (i.e., the race with the highest probability). This can lead to an over-estimate over white voters, as white is the most common majority race in the country, minorities who live in white dominated areas are frequently coded as likely white, while the reverse is less common.
Messaging: Democrats should run on policies that they support and help working Americans, healthcare (option to buy Medicare for all) and taxes (smaller corporate tax cut) to pay for needed infrastructure. Democrats due not need to change any policies, they just need to message what they are doing.
1) Democrats never ran on identity politics, they support civil rights for minorities: I am no fan of the Democratic party's messaging, but the Democrats never ran on "identity politics". Identity politics is how the Republicans have attacked the Democrats for backing the civil rights of minorities. And, Democrats should continue to back those rights, and they have known since the 1960's that backing civil rights was going to cost support from white working class voters.
2) Democratic policies benefit working Americans: Republicans want to repeal ObamaCare and leave tens of million without health insurance; Democrats want to provide option for anyone in America to buy into Medicare. Republicans passed a tax cut moving the marginal corporate rate from 35 percent to 21 percent: by the time the tax cut is fully implemented 83 percent will go to households with income greater than $1,000,000. And, more than half of American households will see a tax increase. Democrats do not need to shift policies, because their policies are already better for working Americans.
3) Trump's of amnesty for undocumented immigrants in US and harsh restrictions on future legal immigration is reasonably popular: which means support for increased legal immigration is scant. But, immigrants, both undocumented and legal are important for our economy, culture, and security. But, no one thinks it is wise for the Democrats to make immigration their key issue of 2018.
4) Democrats need to message their policies: Democrats need to stop micro-targeting messages around policies that have majority support all over the country. They need to have a unified, national campaign showcasing their policies. That way people like the author of this New York Times article will not think the Democrats only policy is whatever the Republicans define the Democrats as.