Former senator and sweater-vest enthusiast Rick Santorum stopped by "The Colbert Report" on Tuesday night where he and fellow Catholic Stephen Colbert discussed the Republican's foray into wholesome movie-making with "The Christmas Candle" and his plans for 2016.

But mostly, they talked about gay marriage.

The conversation, though substantive, was largely cordial, with Colbert eagerly modeling the sweater vest Santorum brought as a gift. The fake conservative host stayed in character throughout the chat, but was nevertheless able to level a pointed critique of his sincerely conservative guest's hard-line stance on social issues, particularly gay marriage.

PHOTOS: Celebrities react to Prop 8 dismissal on Twitter

Colbert opened the conversation by asking Santorum, a runner up in last year's GOP primary, whether he planned to run for president in 2016. He issued a coy non-denial: "I am not... sure."

He also asked Santorum, a vocal critic of the entertainment industry, why he decided to become "part of the problem" in his new role as CEO of the Christian production company Echolight Studios.

"Instead of complaining about what Hollywood is doing we’re going to go out and make movies that reflect the values that I think a lot of Americans still hold," Santorum replied. 

From there, the conversation quickly turned to the subject of gay marriage.

Santorum expressed disagreement with fellow Republicans who think the party should place less importance on social issues, arguing that in fact they could reach out to religious Latinos by standing firm on what he called "biblical principles." 

Colbert jokingly suggested that, with gay marriage now legal in 15 states and the District of Columbia, the country was "riding the rainbow train to Helltown" and social conservatives like his guest were fighting a losing battle. 

PHOTOS: Gay celebrities — who's out?

In news that may come as a surprise to heterosexuals, Santorum said that "marriage has devolved into just a romantic relationship between two people and that’s not what marriage is."

It was this redefinition of marriage as a romantic partnership that does not necessarily involve children that has led gay people to believe they are entitled to wed, Santorum claimed.

“Heterosexuals have lost the definition of marriage and so it’s not surprising that other people see, 'Well, this is what marriage is today and so we should be involved in that.'"

In Santorum's mind, the country needs to “reclaim the institution as a man and a woman coming together to have children and raise them in a way that continues society.”

Santorum was careful with his words, emphasizing marriage as an insitution designed for procreation rather than explicitly denouncing gay people. But Colbert reminded him of the time in 2003 he likened same-sex marriage to a "man on dog" union, comments that prompted columnist Dan Savage to organize a contest that would result in Santorum's longstanding "Google problem." (Interestingly, Santorum's remarks on "The Colbert Report" Tuesday echo what Savage said in a visit to the show two years ago, though the men were, of course, making very different points.)

PHOTOS: Celebrities by The Times

Santorum said his original remarks had been taken out of context, but reiterated that marriage is "a relationship that is important for the continuance of society and that’s what we need to focus on."

With that in mind, Colbert asked Santorum about the "disturbing news that gay people have children."

"I’ve also heard some places they can even adopt children," he said.