In 2011 and early 2012, support for marriage equality was increasing at a rate of about two percentage points per year, while opposition was decreasing at the same rate, for a change in the margin of about four points per year. Following Obama's statement in support of marriage equality, PPP's state polls show an additional change in the margin of about seven points, a substantial jump equivalent to leaping ahead about two years.
Most surprisingly, an increase was seen in all demographics, including conservatives and Republicans. Honestly, I thought support for gay marriage among Republicans would decrease out of sheer contrariness.
Below, you can see a comparison in the change in margin for pairs of state polls where the second poll was completed either before or after Obama's interview.
There's a lot of fine print, but basically on the left, you can see the change in margin from one poll to the next in the same state, usually about six months apart, under baseline conditions where the margin was improving about two points every six months (four points per year). There's a lot of scatter, as expected for polls of this size. On the right, you can see the change in margin for seven states where PPP has asked about same sex marriage after Obama's interview, compared to a poll completed about six months before the interview. Clearly, the change in margin is much greater when the second interview was completed post-interview.
All demographics changing favorably
To look at demographic changes, I used the three-part question (marriage, civil unions, or no legal recognition). To my great surprise, on average even those who described themselves as Very Conservative showed movement, on average, away from the No Legal Recognition position. Democrats and liberals are moving faster, however. And, significantly, the greatest change is among African-Americans.
Each arrow on this graph represents a pair of state polls, one before and one after Obama's interview last month. We want to see arrows pointing towards the liberal corner, in the lower left, or a least away from the conservative corner, in the lower right.
In general, conservatives' opinion is moving away from the conservative corner (lower right) and towards the mushy middle (civil unions, top). Moderates and liberals are moving towards the liberal corner (support for full marriage equality). Moderates and liberals are moving faster, though. (For more on how to read this type of graphs see the section at the end of this post.) Visually, this graph reminds me of small creatures desperately fleeing a threat.
The most dramatic changes were among African-Americans and Other when Other includes African-Americans (in Minnesota, for example). These changes were consistent and large. Each pair of polls has only a small number of African-Americans, but when we see the same thing in poll after poll, we can be confident of the movement.
Instead of many African-Americans abandoning Obama (today's Daily Kos poll shows 90% support against Romney, and the post-interview average is about the same as the pre-interview average), many African-Americans changed their minds on marriage equality. Anecdotally, this was a result of much (ongoing) discussion and argument, and further rapid change in opinion may occur.
Additionally, you can see charts for party, gender, and age. Men changed more than women, and younger generations changed more than older ones. However, on average, all demographics were either moving away from the conservative corner or towards the liberal corner.
This is what it looks like when a President sways public opinion.
Fine print.
NC polls were excluded because of the active campaign there over the past six months. (For the record, they showed an average change in margin of five points, comparing the post-interview poll with each of five pre-interview polls taken of registered voters from September to January.) The period of time between each pair of interviews varied from 4 to 8 months. To find the 'jump' attributable to Obama, I subtracted off the expected change in margin, based on a rate of four points/year, then averaged the results.
How to read these funny charts
To find out the percent that support gay marriage, follow the blue line up and to the left towards the left axis. To find out the percent who think there should be no legal recognition, go follow the red line down and to the left towards the bottom axis. For the middle positions, go straight right along a grey line to the right axis. This axis is labeled Civil Unions, but also includes those who chose Not Sure as a response, as numbers on this kind of chart must add up to 100 and Not Sure is a "mushy middle" response that fits far better with Civil Unions than pro-marriage or anti-everything.
Update: for more analysis see jpmassar's diary.