"We've really used a spirit of relentlessness," says Marc Solomon, the national campaign director for Freedom to Marry. "That's the way we've approached this entire movement from the get-go in Massachusetts and around the country."
Tactics endure after 10 years of same-sex marriage →
"The center of political gravity has shifted for good," said Mr. Solomon, citing polls showing surges in support for gay marriage among Republicans under age 44.
Gay-rights backers woo young Republicans →