No. Sure, MAGA Republicans are only 25-30% of the population, but most of the people share at least some beliefs that would hold the entire nation back. There's widespread economic illiteracy, that leads to people generally favoring monopolies, and not believing in economy of scale in some circumstances. It's an article of faith that the press has a liberal bias. Lots of people distrust elections. There are lots of authoritarians, which is the fertile ground that let Trump take power in the first place.
He did have to leave his independent status and join the Democratic party in order to participate in the primaries. But that was just a formality; he filled out a form.
Some people did vote for him. Just nowhere near a majority. A lot of people resented that, and stayed home rather than vote for the primary winner. So she lost, and the rest is very literally history.
Outsiders can and do win in the primaries. Trump is the most prominent example. He was not a familiar regular, and nobody in the party leadership wanted him.
He won the primary, and went on to win the Presidency. The party leadership came around to support him, and the new leadership is vetted by him rather than the other way around.
Is that a given?