WASHINGTON — IT’S no secret that the Republican Party differs with public opinion on some of the day’s biggest issues. Be it on gun control, immigration, same-sex marriage or high-end taxes, the party has advocated a position at odds with the beliefs of most Americans, polls show. This disconnect has helped Democrats win the popular vote in five of the last six presidential elections.

The recent acrimony in the Texas Legislature, with Republicans pushing a restrictive abortion bill, seems to provide a new example. It has allowed Democrats to cast Republicans, once again, as out of the mainstream.

Yet abortion is not quite like those other issues.

On abortion rights, both parties have a claim on public opinion. Maybe more to the point, both can make a strong case that the other party has an extreme view. Abortion is the relatively rare issue in which the cliché is true: public opinion does actually rest about midway between the parties’ platforms.

As a result, abortion occupies a different place in the Republicans’ continuing struggle about whether and how to modernize their party. On a set of other social issues related to the increasingly diverse American population, the party clearly faces big challenges. The two fastest-growing ethnic groups — Latinos and Asian-Americans — are decidedly liberal. Younger white adults also lean left. My colleague Nate Silver estimates that in the year 2020, ballot initiatives on same-sex marriage would pass in 44 states, based on the direction of public opinion. The only six states where the initiatives would likely fail are solidly Republican Southern states.