DES MOINES — They are angry at a political system they see as rigged. They feel squeezed by immigration, or the power of big banks. They sense that America is heading in the wrong direction, but emphatically believe only their candidate has the strength and vision to change things.

The voters driving two of the more remarkable movements of this election cycle — for Donald J. Trump and Senator Bernie Sanders — share striking similarities. Both groups are heavily white, more male than female, and both are fueled partly by people who, in interviews, express distrust of their parties and the other candidates, especially Hillary Clinton.

No matter how their preferred candidates fare in the Iowa caucuses on Monday, the supporters of Mr. Sanders and Mr. Trump are reshaping the campaign and could have a profound impact on the outcome in the fall.