The possibility of Bernie voters becoming Trump voters was first thought to be because of their common critical positions on free trade agreements which have hammered working people. Bill Clinton as president was responsible for the passage of the Republican-initiated North American Free Trade Agreement. Hillary Clinton as Secretary of State promoted free trade agreements with Colombia and the Trans-Pacific Partnership. Hillary Clinton as candidate has reversed herself but is not trusted. Barack Obama after all ran against NAFTA in 2008 and then as president promoted free trade agreements.
Donald Trump as candidate seems to have learned from Obama that free trade agreements are unpopular with voters and has implied opposition. As president, though, I have no doubt that he would bend to the Republican orthodoxy and support them.
If there's one thing the corporate elites are unified in wanting strongly, it's more free trade agreements which they see as padding their bottom lines. And they expect presidents, whether Republican or Democrat, to get them for them.
Now it appears that there will also be Bernie voters who spurn Hillary for Trump simply because they like him more than her or dislike him less. For them voting is less an act of rational choice than a personality contest. Throw in a dose or more of misogyny and you see some of the problems confronting Clinton's campaign staff as they transition from beating back an unexpectedly strong primary challenge to her left to confronting another unexpectedly strong challenge, this time to her right in the national election.
It's difficult to estimate how big a percentage of voters choose primarily on likeability, but it only takes a small percentage to swing national elections when the electorate is fairly closely divided as is the U.S. one.
Ronald Reagan, the actor and corporate spokesman turned politician, had personal attributes that made him likeable, a crucial asset that helped him to win elections despite poll after poll showing that voters disagreed with his policies. George W. Bush, despite being a nondrinker, was the guy you'd like to have a beer with rather than his opponents.
Trump is liked for his perceived decisiveness, no matter that he has never held political office or whether the positions he decisively pronounces make sense or are held consistently. He is often wrong, objectionable, or inconsistent but never indecisive at any particular moment.
"I vote for the person not the party" is frequently stated by those who vote on the basis of likeability as if it demonstrated profound wisdom or character. Or, a slightly more involved superficiality: "I don't believe in isms."
But parties and "isms"--liberalism, conservatism, socialism, etc.--are much more important for informed political choices than how likeable candidates are. What counts is what politicians are going to do with the power that voters entrust them to exercise; and the only way to determine what candidates are likely to do if elected is to critically and rationally examine what their parties stand for, what the candidates have done in the past, and the ideas they put forth.
Sanders supporters who move to a third party candidate such as Jill Stein of the Green Party are a different matter. They are choosing on the basis of who they perceive to embrace more strongly the issues they care about. It is a rational choice in terms of issues but not strategy. There is nil chance Stein would win but a real chance of the spoiler effect where those votes would benefit Trump in battleground states.
Rejecting Clinton for Stein or another third party candidate is an example of what classic German sociologist Max Weber called rejecting an ethic of responsibility for an ethic of ultimate ends. In the former, decisions are measured in terms of their consequences; in the latter all that counts is the purity of the motive regardless of the outcome.
For responsible Sanders supporters the outcome of this coming national election very much matters. From the point of view of progressive values and wanting to break with a rigged political system, Clinton may be a lesser of two evils, but she is very much of a lesser and the alternative is very much of a greater.