I mean, OK, that was on me for adding that line at the end, & I apologize. But my point still stands, if you want to address it: Does The Party pick the candidate, or does the people's vote count more than The Party's Choice? Ignoring my petty comment, if you are willing to, which is it?
The Party backs the candidate, which can include backing a candidate that obviously has popular support. However, it's not always as simple as one candidate enjoying popular support and the Party then backing that candidate. Trump faced moderate to significant competition in the primaries (for example, from Cruz). That support for Cruz didn't vanish. Nor did any support for other candidates. Some of these may have continued to oppose Trump, but the party as a whole put its weight behind Trump, and as such influenced opinion over time. That's what the resources provided (by the Party) can achieve. I'm not exactly saying "conspiracy theory", this is basic advertising in a nutshell. Of course you want your voter base on board with your candidate.
However a common alternative is "better this jerk than the other person (from the other party)". It's logic frequently thrown at leftists in order to support more centrist or even right-leaning candidates, depending on context. It's used a lot across the spectrum, but it's rarely used leftwards; i.e. to generate support for a leftist candidate against a common enemy (which I find interesting, but it's a bit of a tangent).
So the real question, to me, is whether or not the popular support enjoyed by a frontrunner more important that the Party's choice to invest in that frontrunner and align themselves with them. And obviously this has to be evaluated on a case-by-case basis. I don't think you can generalise. It depends mainly on the candidate, which is where I think you and I might differ. You might think that popular support is what seals it, but I think if the candidate threatens the establishment, then the establishment will go out of its way to (attempt to) reduce support for that candidate.
You can even see it now, with Hillary Clinton cautioning about "going further left". US politics hasn't
gone left. Sure, there are some course corrections from Trump's Republican tenure vs. Biden's current Democratic leadership, but if the end point is still "centre-to-right", citing it as an example of moving leftwards (as some conservatives will claim) is kinda disingenuous. The results are what matter, right? The results are what the Republicans are going to hammer the Democrats with, even if the Republicans are a key part of
why the results are what they are. What Clinton is doing is shaping public opinion. And that's just one example.
So a
tl;dr would be: the peoples' vote often counts, except when the candidate is enough of a threat to the establishment players who prefer the current status quo (and that, ironically,
is bipartisan). The Overton Window in this regard only ever seems to move rightwards, and not leftwards.