Donald Trump is really running on one issue, his hard line on immigration. Some, but not all, of his supporters have gone to him due to this stance. Trump says the things they've thought privately but knew they couldn't get away with saying publicly. They've been told for years that they can't think illegal immigration is wrong because that's racist. Well, now they can. Beyond immigration Trump's support isn't ideological. He doesn't draw specifically from conservatives, libertarians, or moderates. It doesn't matter to many of his supporters what his positions are on issues and many of those positions are hazy. If you're pro-choice you can take past comments by Trump and figure he'll go your way when he's President.
Other than his stance on immigration there's no reason that Trump's supporters can't be firmly liberal or progressive. His supporters are angry at a Washington that isn't working for them but is working for those who are well connected. Trump is telling them that he knows this because he's been well connected and has been able to get government to do what he wants. Elect him and you'll finally have an insider representing you. Trump will make deals with the establishment Democrats, Republicans, and foreign governments. Because that's what he does. And he can't be bought! He'll work for the people who elected him.
Ted Cruz's support is often lumped together with Trump's. And it's true that he has anti-establishment support from people who think Washington isn't working for them. Cruz's supporters are firmly conservative, however, and have firm stances on the issues. And Ted Cruz supports those stances. Cruz is the opposite of Trump in that he's not promising to make deals for the American people. He's promising he won't make deals. He brags that no one in Washington can get along with him. Vote for Cruz and you'll have someone who won't waver from conservative positions. Of course, this is unrealistic. Cruz's supporters claim to support the Constitution. They should realize that there is not only an executive branch but also a legislative branch. These people are also elected. And you have to make deals with them.
Sanders is far closer to the left wing Cruz than the left wing Trump. That makes a lot of sense because Trump takes some support from the left and his support is about competency, not ideology. Like Cruz, Sanders argues that Washington isn't working for you. It's working for the 1%. While Cruz's supporters like it when the Texas senator takes on established Republican groups, Sanders got slapped down for pretty much calling Planned Parenthood insiders. It's okay to fight against Democratic business interests but not Democratic social groups. Sanders promises ideological purity that Hillary Clinton can't offer. Rather than cast other members of his party as the villains, as Cruz, does he casts Wall Street, corporations, and Republicans in those roles. Forget that many on Wall Street and corporations are firmly in the Democratic camp. His supporters think they're all Republicans.
Like Cruz's supporters Sanders' supporters think most of America agrees with them and that the only thing preventing policies they love from being implemented is the small cadre of insiders. When asked how he'd hope to get his policies through a Republican congress, Sanders gives a vague answer that the American people would have to rise up and make it happen. I assume Sanders believes that enough people agree with him that we could have progressive majorities in congress. If only those people would vote.
Part of Barack Obama's brand is his pragmatism. He'll settle for what's possible, not worry about what's not. These candidates are selling making what is impossible possible and that is an incredibly strong draw to the voter. We'll see how it translates Monday in Iowa.