Washington (CNN) Electability, many liberal Democrats will tell you this cycle, is a farce. It doesn't really exist. It's simply a scare tactic used by establishment, centrist Democrats to keep voters from choosing a true-blue liberal for the nomination to run against President Donald Trump in 2020.

And there's some evidence to suggest they're right -- namely Trump himself. Trump's GOP opponents in the 2016 race spent the entire campaign insisting that in nominating the controversial billionaire the party would be forgoing its chances of beating Hillary Clinton in the general election. Then, Trump won. So long, electability!

Except that in a that in a new Washington Post-ABC News poll there's at least the suggestion that who Democrats nominate could make a difference in whether Trump wins a second term or not. Former Vice President Joe Biden leads Trump 53%-43% in that national survey. But Biden is the only Democrat with a statistically significant edge over the incumbent. California Sen. Kamala Harris took 48% to Trump's 46%, while Vermont Sen. Bernie Sanders stood at 49% to Trump's 48%. Trump was tied with both Massachusetts Sen. Elizabeth Warren and South Bend Mayor Pete Buttigieg.

Biden's lead over Trump is explained, somewhat, by the fact that Biden is a wholly known commodity on the national stage -- the result of eight years as Barack Obama's vice president and more than three decades of service in the Senate. Biden is also known -- even by independents and lean-Republicans -- as a centrist, unlike, say, Sanders, who has unapologetically embraced every imaginable tenet of liberalism.

While the next eight months(ish) will decide the electability question vis-a-vis Biden, the takeaway from the Post-ABC poll -- or at least one of the takeaways -- should be that Trump isn't going to be a pushover in November 2020.

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