NEW YORK — By today’s politically polarized standards, the Supreme Court’s momentous Roe v. Wade ruling was a landslide. By a 7-to-2 vote on Jan. 22, 1973, the justices ­established a nationwide right to abortion.

Forty years and about 55 million abortions later, however, the ruling’s legacy is the opposite of consensus. Abortion ranks as one of the most divisive issues in the country, and is likely to remain so as rival camps see little space for common ground.