It now seems likely that Minnesotan voters will vote in 2012 on a constitutional amendment to ban same-sex marriage. If you have been following the national polls and punditry, you might be led to believe that the amendment will probably fail. At this point, however, I would put the money on it to pass. Why?
1. The latest polling (I could find) discovered that more Minnesotans are against same-sex marriage than are for it. The poll from September 2010 found that among likely voters 49% opposed same-sex marriage, while 41% were for legalizing same-sex marriage. Reallocating undecideds based on decided voters (as there is no undecided when it comes time to vote), 54% of Minnesotans are against legalizing same-sex marriage. Some might point to a 2006 poll, which indicated that even though most Minnesotans were against same-sex marriage, they would vote against a constitutional amendment to ban it. The fact is that polling before the California's infamous Prop. 8, a constitutional ban against gay marriage, polling suggested a similar split*: a number of Californians who were against same-sex marriage would vote against Prop. 8. In the end, most voters against same-sex marriage, but also against the amendment, voted for Prop. 8. I would expect a similar trend in Minnesota. 2. Minnesotan demographics indicate that the amendment is likely to pass. Take a modification of Nate Silver's same-sex marriage model that controls for a state's religiosity, a state's median voter's level of conservatism on social issues (with -2 being very liberal to 2 being very conservative), the year of the election, whether the election was held during an off-year or non-Presidential primary, and whether the ballot measure sought to ban same-sex marriage and civil unions or just same-sex marriage. 64% of Minnesotans consider religion to be an important part of their lives; Minnesotans' tend to be quite moderate on social issues (with a score of -.08); 2012 is 15 years after the first gay marriage amendment nationwide; 2012 is not an off-year; and, the measure seeks only to ban same-sex marriage. Given these variable values, the model projects the marriage amendment to pass with a little over 56% of the vote (quite close to the 54% polling number above).
Ah, but only if it were so easy to predict. Points 1 and 2 come with some caveats that deserve explanation.
1. Like the rest of the nation, support for same-sex marriage legalization seems to be increasing. In the aforementioned 2006 poll, only 29% of Minnesotan voters** supported gay marriage, while 54% opposed. That means that in 4 years, support climbed 12%, while opposition dropped by 5%. If that trend continued over the next 2 years, we'd be looking at an electorate that evenly split on the marriage question come 2012.
2. The demographic model has a within dataset margin of error at 95% of about +/- 8.3%. The model is telling us that it is not unreasonable (even if unlikely) that the Minnesotan same-sex marriage ban fails with 49%. For Maine's 2009 same-sex marriage referendum, the model out-of-dataset forecasted the ban to fail with a little greater than 47% of the vote, but it actually passed with a little less than 53% of the vote (an error of about 5.5%).
Keeping these qualifications in mind, I should drive home the point that past history does not look too kindly upon the pro-same-sex marriage side.
As I had previously found and Patrick Egan has expanded upon, same-sex marriage ballot questions tend, if anything, to do worse on election day than pre-election polls predict. In fact, Egan found the bans ("yes" side) picked up, on average, 7% support from the final polls, while the "no" side picked up no appreciable support. In Minnesota, therefore, we might expect the ban to pass in the high 50's, instead of the 54% projected above.
Further, Egan demonstrated that campaigns have little effect on the outcome. The polls six months before the election occur were about as accurate as those right before the election. While October 2010 is far more than six months out from 2012, I would imagine that the swing in favor of same-sex marriage (and against the ban) will probably not advance to the point that two sides reach equality in vote share as spoken about above.
Given all this information, the ban side seems to have the edge. The election will not take place until 2012 and many things may change. Minnesota may defy the trend, but I would not count on it.
* The two situations are not exactly similar, however. Without the constitutional amendment, California would have continued to allow same-sex marriages. Even if the marriage amendment fails in Minnesota, state law bans same-sex marriage. Perhaps, more of the "no to marriage, but no ban" folks will vote against the amendment in Minnesota.
** The sample population for the two polls are not the same. The 2010 poll employed a likely voter sample, while the 2006 sample utilized a registered voter model. 2010 was a very Republican year, so it is probable that the electorate was more liberal in 2006 and is more liberal in 2012. That makes the gains in support of same-sex marriage between 2006 and 2010 more impressive and means that new polling for 2012 might reveal a closer election than the 2010 poll indicated.