Same-sex marriage joins obamacare as the two most important social issues the United States Supreme Court will consider this term.  The decision in both matters may well come down to just one person.

The first case, United States v. Windsor, considers whether the federal Defense of Marriage Act, which defines marriage as the legal union of one man and one woman under federal law, violates the equal protection guarantees of the Fifth Amendment. The second case, Hollingsworth v. Perry, involves California’s Proposition 8, a voter-approved ban on same-sex marriage passed in 2008.

Although Supreme Court justices are required to rule on the legal issues and evidence before them, they do not make decisions in a vacuum. Therefore, many are speculating whether the changing tide of public opinion in favor of same-sex marriage will sway the Supreme Court.

Just this November, voters in Maine, Maryland, and Washington approved laws legalizing same-sex marriage. They became the first states to approve the unions via the ballot box, rather than through a legislative amendment or court order.

The growing acceptance of same-sex marriage highlights that the American public will accept a Supreme Court decision striking down California’s same-sex marriage ban or overturning DOMA. However, voter approval could also cut the other way.

The increasing number of states legalizing same-sex marriage on their own could be used as evidence to support arguments against addressing it on the federal level. Opponents like the National Organization for Marriage are already pointing to the election results as proof that states can and should be allowed to work through the issue on their own. They also point to the growing acceptance of same-sex marriage as proof that discrimination is against gay, lesbian, bisexual and transgender Americans is waning.

Nonetheless, the Supreme Court has shown a willingness to step in to protect equal rights, regardless of where the American public or the states stand on an issue. In the 1967 decision of Loving v. Virginia, the Supreme Court struck down bans on interracial marriage. At that point, only 16 states still prohibited marriage between blacks and whites. However, 70 percent of Americans opposed such unions.

Justice Roberts was the deciding vote in the obamacare case last term.  Will he be the person who ultimately decides the fate of same-sex marriage?   

Donald Scarinci is a managing partner at Lyndhurst, N.J. based law firm Scarinci Hollenbeck.  He is also the editor of the Constitutional Law Reporter and Government and Law blogs.