The amicus briefs filed with the Supreme Court representing the Democrats and the Republicans are painting a very telling picture regarding which side is winning with these briefs. The winning side, by an overwhelming margin, is the pro-equality side.
Pink News points out the massive discrepancy between Democratic support and Republican opposition:
In a sure-fire sign that some Republicans don’t want to be seen on the wrong side of history in the case, just 57 out of the party’s 299 Members of Congress signed the brief, which argues states should be allowed to decide if gays are allowed to marry.
[...]
Meanwhile, a brief from the Democrats in favour of equality was signed by 211 of the party’s 232 Members of Congress – with 167 House members and all 44 of the party’s Senators signing.
This means that we have one party overwhelmingly in support of nationwide marriage equality and party overwhelmingly not in opposition to it.