They didn't have a single populist in the beginning. They just had "Tea Party Republicans". Unfortunately, this new "flavor" of conservative was even more racist and unintelligent than the original recipe.

Their voters immediately gravitated towards them, because they were seen as relatable outsiders, whose biggest policy position was to do whatever it took to hurt "the left", and/or anyone who even suggested the idea of "working together" with them. (ie. RINOs)

Trump just eventually took advantage of this movement and declared himself its leader. But when it first started, he still considered himself a Democrat.

It's a representative democracy...which means you need to flip seats in Congress in order to take over a party. That's all. It's a gradual process, but one that is entirely possible within the current system. We the people, have the power to do this, just by voting.

The biggest problem is, that progressives are fighting against the money. Tea Party Republicans didn't have that problem, since most of their socio-political ideology aligns with Libertarian policies. No taxes, no regulations, no corporate accountability. That draws a lot of support from the kinds of people who were already dissatisfied with the compromise Democrats and Republicans had struck between the elites making more money, and the consumers they use to make it.

The Tea Party and later MAGA are all in on fucking us all over to benefit the ruling class. Most of their voters are just too gullible to realize that. They think they're somehow "sticking it to the elites", by giving them everything they could have ever hoped for.

In many ways, it was never a real grassroots movement. It was always just an astroturfed effort. But it demonstrates how you can fundamentally change the entire direction of a party in US politics. One seat at a time...until the new majority votes the way you want them to.