Election Impact of Shifting Voter Support
If white, working class voters in Southern states and rural districts flipped to progressive causes, Democrats are more likely to win for both down-ballot races as well as the presidential election. Below we will discuss our research in more detail.
Elections are notoriously hard to predict. Voter turnout and support for a candidate are two important qualities that are difficult to predict and measure. The election in 2016, when Donald Trump beat Hillary Clinton, is a clear example of this phenomenon. Most pollsters incorrectly expected Clinton to win by a large margin.
The difficulty in predicting elections is precisely why answering the impact on working class white rural voters shifting their support to progressive issues and candidates is difficult to answer. The question is essentially asking to predict what would happen if a social class largely reverses their politics within a few months. Thus, scholarly sources that directly answer this question do not exist.
To answer your question, we built an answer based on a paper that studied the working class white vote in 2012 and 2016 via probability and linear regression models as well as data from research organizations such as Pew. While we cannot specifically answer what would happen if rural working class whites reversed their political opinion, we can discuss a "what if" based on what we know from three of the last four major elections.
Impact of Flipped Working Class White Voters
President Obama in 2012 won 27.2% of the working class white vote as a whole according to research by the sociologists Stephen Morgan and Jiwon Lee. Using a linear regression model, Morgan and Lee found that president Trump won about 30% of the white working class vote as well. President Trump also engaged white working class voters who abstained from voting in 2012. About 58.5% of working class whites who did not vote in 2012 turned out to vote for president Trump in 2016. Morgan and Lee note that a "substantial portion" of working class whites who voted for Obama switched their vote to Trump in 2016.
In other words, Obama and Trump both gained a substantial portion of the working class white vote. While this is not the only criterion for victory, candidates in both presidential races and down-ballot elections increase their probability of winning by engaging working class whites. Progressives in the 2020 election would require a similar flip as Obama experienced in 2012. To answer your question directly, if enough working class rural whites flip their politics (at least for the election), then the probability of progressives winning the respective congressional seats or presidential candidates winning said district increases. Obama in 2012 is the clearest example of this phenomenon. However, his case was not limited to the South, but other states.
In both down-ballot and presidential elections, whites (i.e., in general not just working class whites) make up a large portion of the electorate. Democrats and progressives often rely on support from minority voters as well as whites in order to win elections. However, galvanizing minorities to vote is sometimes difficult. This makes it difficult for progressives who need a coalition of whites and minorities to win elections, especially considering that white voters, especially working class whites, often vote Republican.
Recently, in the 2018 midterms, Democrats increased their share of white voters. This is similar to how Obama increased his share of white voters, which allowed him to take states that were purple or lightly red in 2012. Progressives in 2020 would likely be required to flip enough whites, working class or not, in order to win congressional elections or the presidency.
While your question focuses on rural working class whites specifically, college educated whites are much more likely to vote for Democrats or progressives than rural working class whites. However, working class whites may benefit from progressive and Democratic policies such as those that focus on labor rights and equity. Thus, progressive candidates who solidify a base of minorities as well as a threshold of working class whites would likely win their elections in 2020. According to research from the Brookings Institute, the turnout rate for minorities was 38% in the 2018 midterms, which is the highest rate recorded thus far. Progressives who manage to flip a threshold of working class whites could build a winning coalition for 2020.