A common piece of conventional wisdom — and one that has backing in the political science literature — is that candidates are punished for being ideologically out of step with their constituents. This is what underlies the usual advice given to presidential candidates in a general election: move to the center, or risk being perceived as too ideological. Thus far in 2016, as Matthew Atkinson and Darin DeWitt have argued on this blog, prediction markets bear out this advice.

Now here’s something fascinating about this election cycle: Republicans seem not to believe that there is any electoral penalty for being strongly conservative. But Democrats do believe a strong liberal will be penalized.

That’s the conclusion from the newest Huffington Post surveys of Republican and Democratic activists. These surveys asked activists to rate their party’s candidates on a five-point scale ranging from “very liberal” to “very conservative” and also to check a box beside any candidate who “is capable of winning the general election for president” assuming that this candidate did win the nomination.

Let’s focus only on candidates with some minimal shot of being nominated — which I’ll define as candidates who at least 20 percent of activists believed were capable of winning the nomination.

For Democratic activists, that’s three candidates: Hillary Clinton, Joe Biden, and Bernie Sanders. Below is a graph that compares the percentage who said those candidates were “very liberal” to the percentage who said those candidates could win the general election.

Although Sanders is perceived as more electable than in the last Huffington Post survey of Democratic activists, he is still perceived as less electable than Clinton and Biden. In turn, both Clinton and Biden are perceived as more centrist than Sanders — mostly as “liberal” or “moderate” instead of “very liberal.”

Of course, this is a comparison among only three candidates. And we don’t know that Sanders’s electability deficit is necessarily due to his perceived ideology. But the correlation is at least consistent with what political science research has shown.

Now compare what Republican activists said about the electability and perceived conservatism of the nominees:

There is no relationship here. These activists see Donald Trump, Ben Carson, Marco Rubio, and Carly Fiorina as equally electable, even though they see Carson as more conservative. Moreover, the candidates perceived as most moderate — Jeb Bush and John Kasich — are perceived as the least electable, and even less electable than Ted Cruz, who was perceived as the strongest conservative.

Why would there be this difference between Republican and Democratic activists? I don’t think there’s a single clear answer. It could reflect the stronger emphasis on ideology among Republicans generally. It could also reflect frustration with the liberal policies of the Obama administration, and thus the hope that the candidates most devoted to reversing those policies really do have a good chance of winning.

Now, is it impossible that a strong liberal or conservative could win the presidency? No, it’s not literally impossible. It would depend on conditions in the country in 2016, who the other party’s nominee was, and maybe other factors. If there was a massive recession in 2016, a candidate like Cruz could win, despite whatever penalty he might suffer among moderate voters in the general election.

The point is just that nominating a strong ideologue — whether liberal or conservative — puts a party at risk in November. The question is whether Republicans will begin to appreciate that.