It also means that they should consider the likelihood of their nominee actually being able to pass, and pay for, their legislative priorities. If the Democrats don’t win a majority in the Senate in 2020, then not only is a Warren or Sanders Medicare for All plan a nonstarter, so too is the public-option healthcare plan advanced by candidates like the South Bend mayor, Pete Buttigieg, and former vice-president Joe Biden.

Even if the Democrats gain control of the Senate, they will need the support of conservative Democratic senators like Kyrsten Sinema of Arizona and Joe Manchin of West Virginia. Such senators are likely to balk at the huge tax packages that would be needed to finance the multiple trillion-dollar programs of healthcare reform, student loan forgiveness, free public college, clean energy and other initiatives advanced by several moderate as well as progressive candidates. To expect billionaires alone to pay for all of this is quixotic – particularly since every progressive I know fully expects that billionaires and their lawyers would find some way of weaseling out of whatever taxes might come their way.

A critical attribute of leadership is the avoidance of overpromising. The Republican party has come to grief in recent years because its leaders promised their base that if given congressional majorities as well as the White House they would usher in a rightwing utopia. But they failed because it’s impossible to govern in a divided society without engaging in bipartisan negotiation and compromise.