Is there a mainstream populist party on the right besides the Trump GOP?

Mainstream American politics feel stuck at the extremes. It creates a strange disparity for people in the middle—like a conservative Democrat or a moderate Republican who doesn’t align with their party's current national rhetoric.

Populism is massive right now, but it feels completely tied to the two major brands.

Are there any active, mainstream third parties on the right (or even the center-left) that offer a true populist alternative for voters who feel alienated by both Trump and the progressive left?