There’s reason to believe this party gap might be misleading, however. It turns out that when you ask people about specific conditions — the details about abortion decisions — support for abortion erodes and party differences disappear, even among those who previously said abortion should be legal under all circumstances. And the opposite is true, too — in some cases, opposition fades and leniency is extended.

Based on work done by the Stanford political scientists Morris Fiorina and Jon Krosnick, the A.N.E.S. fielded a more specific battery of questions in 2012, using seven different circumstances to ask whether respondents believed abortion should be legal or illegal or whether they weren’t sure. The idea was to uncouple the conditions of rape, incest and risk to the life of the mother from one another to learn about support for each of these categories separately and for some others.

For example, the A.N.E.S. asked people if they favored or opposed the legality of abortion if staying pregnant would cause a woman to die. Across the parties, overwhelming majorities (nearly 70 percent of Republicans and 80 percent of Democrats) agreed that abortion should be legal in this situation.

Another question was whether abortion should be legal if the child were not going to be the sex the woman wanted it to be. Across the parties there was a clear pattern: Hardly anyone in the United States (only 5 percent of Republicans and 10 percent of Democrats) believed abortion should be legal in this case.