Nate Silver crunches the numbers of increasing support for marriage equality in various states. Here's his conclusion:
The state has roughly average levels of religiosity, including a fair number of white evangelicals, and the model predicts that if Iowans voted on a marriage ban today, it would pass with 56.0 percent of the vote. By 2012, however, the model projects a toss-up: 50.4 percent of Iowans voting to approve the ban, and 49.6 percent opposed. In 2013 and all subsequent years, the model thinks the marriage ban would fail.