Washington (CNN) The fault lines in the 2020 Democratic presidential primary are clear when it comes to health care.

On one side are Sens. Bernie Sanders (Vermont) and Elizabeth Warren (Massachusetts) who support "Medicare for All," a proposal that would eliminate the private health care industry totally and replace it with a government-run system. On the other side are former Vice President Joe Biden and South Bend Mayor Pete Buttigieg, both of whom have said the best course of action is to improve upon the current law of the land -- the Affordable Care Act -- rather than undergo a(nother) wholesale change in the health care delivery system.

In the districts Abramowitz examined -- places President Donald Trump won in 2016 by less than 10 points that were either open seats or a Republican incumbent -- just 42% of Democratic candidates who publicly supported Medicare for All won in 2018 while 72% of Democrats who did not support the legislation came out on top.

Obviously, it is not as simple as that. House races aren't solely decided by where a candidate stands on a single issue -- even one as high-profile and intensely felt as Medicare for All. But even when Abramowitz ran a regression model to control for other factors in these five dozen most competitive contests, he found similar results.

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