Forgive me if these points have been raised before but I've not read the full thread, what with house moves, Christmas and needing a bit of time to consider matters after the disastrous UK election results.
However, I would issue a couple of cautions against drawing simple conclusions from our experience in the UK.
The first is that there are, of course, multiple reasons why we (Labour) did so badly in the elections, but their precise nature is still a matter of heated ideological debate.
There's also the point -- very often forgotten -- that in parliamentary democracies, you vote not for the Head of Government (Prime Minister) but for the local Member of Parliament.
Obviously, by voting for your local MP, you're sometimes voting for (or against) the next government and PM too (though not always, by any means -- no one voting for the SNP or PC expects their party's leader to become PM since they run candidates only in Scotland and Wales).
However, even when you do vote for a candidate whose party leader may become the next PM, that's only one consideration -- I live in a Labour-held English marginal constituency, so my vote might, indirectly, have resulted in Jeremy Corbyn as PM, but my vote was very much for my local MP, for whom I have a very high regard, rather than for Corbyn.
In other words, I voted Labour despite the fact Corbyn was leading the party, not because he was leading it.
Similarly, I think the party has to have a manifesto that seems attractive and coherent to the voters, which Labour's certainly wasn't. We had plenty of attractive policies, certainly, but the overall impression was that we were getting a confused wish-list, not a thought-out and costed reform programme that stood any chance of being implemented in the next five years.
So, I think my advice would be not to make the mistake of assuming that everyone hates the other side's leader as much as you do, and not to make the similar mistake of assuming that everyone likes your leader quite as much as you do, either. Few voters here were in any doubt about Boris Johnson's many faults, but neither were they in any doubt about Corbyn's many defects, either.
Furthermore, I think the US Democrats have to go into the elections with an attractive and credible programme for the next four years that they feel comfortable urging upon the voters, and which voters can support, too.
"Vote me because I'm nowhere near as bad as the other guy" is not an election winner, even when it's true.