The massive defeat for Jeremy Corbyn and the Labour Party in the United Kingdom, and Prime Minister Boris Johnson gaining legitimacy for Brexit, is a shock that might be a strong warning to the Democrats for the Presidential Election of 2020.
It IS possible that Donald Trump could win a second term, and IF Bernie Sanders or Elizabeth Warren were to be the Democratic nominee, portrayed as too far to the left, that could be the result.
It could be that this promoted the moderate centrist view–that Joe Biden, or Pete Buttigieg, or Amy Klobuchar–might be the best choice for the Democrats.