As Americans steadily warm to the idea of same-sex marriage, and as the Republican Party embarks on a big rebranding effort, there has been increasing speculation about what line the GOP will ultimately draw on marriage equality.

Despite the dramatic shift in public opinion over the past few years, though, a number of recent signs demonstrate just why the GOP will likely remain steadfast in its opposition to same-sex marriage. 

An NBC News/Wall Street Journal poll released Friday found that 53 percent of Americans now support same-sex marriage while 42 percent do not, a split roughly in line with the findings of other recent polls on the issue. Seventy-three percent of Democrats said they supported gay marriage, as did 54 percent of independents. An overwhelming number of Republican respondents, however, said the opposite; fully two-thirds of them opposed allowing gay couples to wed.

In addition, the survey suggested that Republicans' opposition may be linked to an unchanging view about society's role in fostering tolerance.

When asked whether it was more important for society to "[promote] greater respect for traditional social and moral values, or to [encourage] greater tolerance," 44 percent of respondents chose tolerance, up from the 29 percent who said the same back in 1999. That significant spike came despite overall Republican opinion on the topic remaining virtually unchanged over the same time period: In 1999, 76 percent of Republicans chose traditional values over tolerance. Today, 77 percent said the same.

"This movement by Democrats and the non-movement by Republicans might very well represent the biggest difference between the two political parties, especially when it comes to social issues and values," says NBC News, which declared that the poll showed how "Republicans are from Mars and Democrats are from Venus."

Those findings come as the Republican Party has struggled to balance two competing interests: Its desire to craft a gentler, more inclusive message, and its need to placate the social conservatives who make up a powerful wing of the party. 

Almost immediately after Republican National Committee Chairman Reince Priebus announced the findings of the party's autopsy report — a self-evaluation released in March advising the party to convince gay voters that, "we care about them too" —  conservatives struck back. Mike Huckabee and Newt Gingrich have warned that a policy shift on marriage could split the party in two, while Rick Santorum recently remarked that it would be "suicidal" for the party to embrace gay marriage.

Then on Thursday, Tony Perkins, president of the prominent Family Research Council, cast his lot with that growing movement, urging Republican donors to withhold financial contributions until the party affirms its commitment to traditional marriage. 

"Until the RNC and the other national Republican organizations grow a backbone and start defending core principles, don't send them a dime of your hard-earned money," Perkins wrote in an email to supporters of his organization, according to CNN, who obtained a copy of the letter. "If you want to invest in the political process, and I encourage you to do so, give directly to candidates who reflect your values and organizations you trust-like FRC Action." 

Twelve other groups joined Perkins earlier this week in sending a stern letter directly to Priebus ahead of the RNC's quarterly meeting in Los Angeles, asking him to pass a resolution reaffirming the party's opposition to marriage equality. 

"We respectfully warn GOP Leadership that an abandonment of its principles will necessarily result in the abandonment of our constituents to their support," they wrote in a letter, first obtained by NBC News.

The RNC will consider that resolution on Friday. 

For his part, Priebus has signaled that he's in no rush to move the party in a new direction. He has lauded Huckabee as a "model" on the marriage debate, and walked back parts of the autopsy report, saying that its more controversial aspects could be ignored.