there's this debate they're having over whether they need to appeal to the centre or the fringe, and it's something i'm kind of qualified to comment on.
the actual, technically correct answer is that the debate suffers from definitional problems; the kinds of voters that klobuchar is imagining are purplish swing voters are actually historical democrats, through and through, who feel the democrats have turned on them. and, they're not wrong. it follows that the best way to appeal to republican support is to campaign on the left.
i'm talking about voters in pennsylvania, in michigan, in wisconsin...and also in minnesota and in ohio. these people didn't vote for trump because of his messaging on immigration, because of his evangelical phoniness, because of his tax policies or because of any of the other things that we associate with the republican party. they voted for trump because they thought he was less dangerous than clinton - on trade, on foreign policy, on health care and on other issues that historically are associated with democrats.
and, on some of these issues, they were stupid, and they need to be told as much. on others, trump has arguably been less evil than clinton would have been expected to be, and the arguments you hear coming from biden, and sometimes even from sanders, just exacerbate the point as to why they lost.
but, the party has been so out of touch with these voters for so long that they can't even define them any more, and it's an open question as to whether they're even still in play.
the flip side of this is that the voters they need to win in the south - blacks, catholics, and disgruntled whites, too - are actually much more in the description of what a klobuchar imagines exists in wisconsin (and in truth doesn't). if you want to win the south, you run on the right. that should be obvious...
so, there's this weird disconnect where you have the sanders people arguing that you need to run on the left, and then going after demographics that are dominated by conservative values, and you have the klobuchar people arguing that you need to run in the centre, and then mostly going after white liberals. but, it demonstrates the broader point - wherever you are on the spectrum, you need to convince people beyond your base. that's what the job is.
what's the answer? well, you want to maximize your vote totals, which means avoiding thinking in dichotomies. these propositions are not mutually exclusive, you can and must do both at the same time. and, there are challenges on both sides of this, but i might point something out - it's easier to convince a registered voter to vote than it is to register a new voter.
if you want to win back the trump-obama swing vote, the key is to focus on union issues.