The GOP's same-sex marriage evolution: A slow, choppy tidal shift

Thom Tillis has helped ink plenty of bipartisan deals over the past two years. His advocacy for protecting same-sex marriage rights still surprised some of his fellow senators.

“When people first saw me get involved, they were scratching their heads,” the North Carolina Republican said in an interview just before the marriage bill passed the Senate on Tuesday.

The second-term Tillis saw the opportunity to put his own mark on an issue central to LGBTQ rights just a few weeks after he leaped into summertime gun safety negotiations that divided...