Massachusetts Democrats organized an open letter to Brown urging him to use his appearance with Christie as an opportunity to declare support for gay marriage, but there was no indication Brown would oblige.

Meanwhile, the political arm of the National Organization for Women, a feminist group, endorsed Warren, the front-running Democrat seeking to unseat Brown in November. The group's political action committee called Warren an advocate for economic justice and praised her ability to stand up to the "old boys club."

"Warren is a strong supporter of feminist issues, including reproductive justice, women's economic security, constitutional equality and equal marriage rights," said NOW-PAC Chairwoman Terry O'Neill. "She is not only fearless and fiercely intelligent, but also gifted at explaining complex issues in plain language and winning people's trust."