New York Gov. Andrew Cuomo was the first major 2016er to pass a gay marriage bill back in the summer of 2011.

Eight months later, Maryland Gov. Martin O’Malley followed suit with his own same-sex marriage signing.

Now Colorado Gov. John Hickenlooper – a second-tier, potential darkhorse 2016 contender – gets his turn in the spotlight.

With state House passage of legislation to allow gay couples to form civil unions, it now goes to Hickenlooper for his signature.

Going back to his days as Denver mayor, Hickenlooper has long been a proponent of gay rights, but he’s also drawn the line at civil unions, which may not be good enough for progressives who see marriage as the only acceptable measure to attaining real equality.

In fact, Hickenlooper once ran an ad on behalf of an initiative cementing marriage as between “a man and a woman.”

“It’s not marriage,” Hickenlooper says in the spot. “It’s basic legal rights.”

Hickenlooper’s adamant push for civil unions has been branded as bold and historic in Colorado, but one could foresee O’Malley or Cuomo making a pointed distinction on the difference in the midst of a heated primary. And the quote Hickenlooper delivered above could be ripe material.

Colorado-based Democratic consultant Laura Chapin notes that gay marriage is unconstitutional in Colorado thanks to Amendment 43, so Hickenlooper would need to champion a ballot measure to undo it.

“Civil unions is the best you can do right now,” Chapin said. “If the Supreme Court overturns the Defense of Marriage Act, then we can challenge Amendment 43. Hick made civil unions a priority in his opening State of the State address and has publicly and repeatedly stated his support for equality ever since. This is a plus for him in Colorado and elsewhere.”