Three state House Republicans voted to legalize gay marriage in Illinois last year, breaking ranks with their party and giving Democrats just enough support to pass the legislation. All three are still standing Thursday despite an intense effort from social conservatives to defeat them in GOP primary voting.

(AP Photo/Mathew Sumner)

"If you wanted the takeaway to be that voting for gay marriage for an Illinois Republican is the kiss of death, you can't make that case," said Kent Redfield, a University of Illinois at Springfield​ political scientist.

The campaign served as the latest front in the Republican Party's ongoing internal fight over gay rights. Same-sex marriage advocates in the GOP see what happened in Illinois as another sign the ground is shifting in their favor, while opponents cast it as evidence that Republicans who support gay marriage won't go unchecked.

Of Tuesday's winning trio, state Rep. Ron Sandack (R) was the most significant. Challenger Keith Matune conceded to Sandack Wednesday, a day after the incumbent squeaked out a narrow victory that for a time looked like it was headed to a recount. Sandack's vote for gay marriage became a central focus in his race, which was flooded with money and resources by outside forces on both sides.

Sandack received financial support from Paul Singer, the billionaire hedge fund manager protecting Republicans who support gay marriage with his pocketbook. Singer donated to Sandack's campaign and also gave thousands more to Illinois Unity PAC, which supported Sandack.

Matune opposed gay marriage and was backed by conservative groups Liberty Principles PAC and Illinois Family Action. The former is headed by conservative radio host Dan Proft and funded heavily by Richard Uihlein, who founded the packaging company Uline.

Elsewhere on Tuesday, state Rep. Ed Sullivan easily won his primary, in which his vote for gay marriage was less of an issue than it was in Sandack's. Still, it was on the radar, as Singer also gave him money. Sullivan was targeted by an Illinois Family Action mailer featuring two men kissing. "You can kiss the GOP goodbye with officials who vote like Democrats," it said. Sandack faced the same attack.

State Rep. Tom Cross was the only other Republican to vote for the gay marriage law that will go into effect in June. He comfortably won the Republican nomination for state treasurer.

Gay marriage advocates said the three won by campaigning on multifaceted platforms and refusing to allow the opposition to use the marriage debate as a divisive issue.

"I think for anyone ​considering using marriage equality as a wedge issue in 2014 or 2016, it should give those individuals pause," said Gregory Angelo, executive director of the Log Cabin Republicans, a gay rights group.

But gay marriage remains among the most sensitive topics in the Republican Party, even as more and more states are legalizing it, the public has shifted heavily in its favor and the GOP donor community has vouched for it. Only a handful of Republican senators support same-sex marriage publicly. The Republican National Committee reaffirmed its opposition last year. Sandack, gay marriage opponents say, would never have experienced such a close call if not for his vote.

"The takeaway is, you vote for same sex marriage, you are going to have a serious primary," said Brian Brown, head of the National Organization For Marriage, a group that opposes gay marriage.

Republicans have paid a price for supporting gay marriage in the past, perhaps most notably in New York where a trio of state senators who supported gay marriage arguably lost their jobs as a result. But gay marriage advocates hope Illinois will help the party turn the page.

A generational divide may march the GOP toward embracing gay marriage more and more. A Pew Research Center poll showed that 61 percent of young Republicans favor same-sex marriage.

This much is clear: The issue is far from settled in the Republican Party. Illinois was proof of that.