America is very unlikely to turn from a health care model based on private insurance companies to one in which the federal government decides the costs of every medical procedure. The Mexican government almost certainly won’t build a huge border wall to keeps its citizens from entering the United States, particularly when the American president is demanding it.

While they aren’t admitting it publicly, it’s likely that Bernie Sanders (government-run care) and Donald Trump (the wall) understand these proposals are far-fetched. But Sanders and Trump are running for president with a different model than many of their rivals. They are campaigning on themes and values, not policy.

Viewed as policy ideas, Sanders’ proposals to create a single-payer health care system, make college tuition free and break up big banks are problematic. They are very unlikely to be adopted, particularly if Republicans remain in control of Congress.

And Sanders’ ideas, while expansive and far-reaching, may not even be the best tools to address the underlying problems.To expand access to college, many experts favor policies, such as what Hillary Clinton is proposing, that focus on targeting money at low-income students who truly can’t afford higher education without government help. Universal, free tuition at public colleges, as Sanders proposes, would likely end up subsidizing school for kids whose parents could easily afford to pay for it.

Similarly, it’s not clear that a temporary ban on Muslims coming to the U.S and the mass deportation of undocumented immigrants, Trump’s major proposals, are ideal solutions. The number of people coming to the United States from Mexico is already declining. And as many key figures in both parties say, the U.S. government linking with the overwhelming majority of Muslims here and abroad who oppose terrorism is more likely to be effective than a policy that appears to punish one for practicing Islam.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Sanders and Trump’s rivals often make these kinds of details-based objections. Hillary Clinton rightly notes that the Affordable Care Act barely passed, so single-payer has no chance. Jeb Bush and Marco Rubio say it is simply unrealistic to propose to deport millions of people, even if you are a strong opponent of illegal immigration.

Sanders and Trump are also often dinged by the media and their opponents for not offering enough details on their policy proposals. Trump has released the fewest policy plans of any candidate in the race, just 5, compared to 32 from Rubio and 26 from Clinton.

Sanders has 19 plans, but many of them are very big ideas that are not well detailed. He used just 8 pages to describe his single-payer proposal, one of the most radical ideas from any of the candidates. Many questions were left unanswered.

And he offered those details only because Clinton and the press were browbeating him for being too vague.

But Sanders and Trump aren’t running as policy wonks. Sanders has one big idea: the wealthy are taking over the country. Trump, too, is marking a core argument: America is ignoring big problems, like too many immigrants being here illegally and Muslims entering the U.S. who could commit terrorism, because the country is too focused on being inclusive and tolerant.

These themes underline each man’s candidacy, unify their policy proposals and provide a shorthand for their supporters. Single-payer, for the Sanders’ campaign, isn’t just a way to get people more health care. It would specifically weaken or eliminate health insurance companies, big pharmaceutical firms and hospital networks, the kind of big, organized interests that Sanders wants to fight. A government-run health care system would make America less capitalist and more socialist.

The broad goal of gutting an existing health care system that provides huge wealth to some individuals and companies, to Sanders, is in some ways more important than the details of how exactly he would do that.

Banning Muslims isn’t just an anti-terrorism proposal for Trump. It represents an aggressive attack on what many conservatives view as excessive “political correctness.” It shows that Trump, if he were president, would be willing to forcefully oppose affirmative action, Black Lives Matter, Planned Parenthood and any group whose appeals are based in part on advocating for some kind of underrepresented part of American society. Trump is running as a kind of spokesman for white men wary of their views being ignored in a more diverse America.

While proposing ideas far outside of the political mainstream, Sanders and Trump have surged in polls and been much stronger candidates than expected. In part, this suggests they are skilled politicians who saw obvious weaknesses in their opponents and political coalitions in their parties that weren’t well-represented. It was clear when the campaign started there was room to Clinton’s political left and to Jeb Bush’s right.

But their insurgent candidacies also show the value in having a clear, thematic message. Democrats often describe Trump’s appeal in one word: racism. Republicans harp on the fact that Sanders is a self-described socialist, although his views are close to the left wing of the Democratic Party.

Agree with them or not though, everyone knows exactly how Sanders and Trump want to change the country. And those clear, simple themes have been central to Sanders and Trump building the coalitions that have turned them from underdogs to potential nominees.