Washington (CNN) The Human Rights Campaign, which was at the center of years-long efforts to legalize same-sex marriage, has endorsed Hillary Clinton's presidential bid.

While not entirely unexpected, the endorsement is a win for Clinton, shoring up her left flank with support from a key Democratic demographic.

While some critics have said Clinton's support for same-sex marriage took too long to arrive -- she said she personally supported same-sex marriage in 2013 and then later said it was a constitutional right in 2015 -- Clinton has made LGBT equality a part of her stump speech and she's repeatedly championed the Supreme Court's same-sex marriage decision last year.