On his blog, FiveThirtyEight.com, Silver predicted the presidential election popular vote within one percentage point — predicting 49 of 50 states’ results correctly. He also predicted all of the resolved Senate races correctly. His polling success brought him exposure in such news outlets as The Wall Street Journal, Newsweek, CNN, MSNBC and PBS’ “NewsHour with Jim Lehrer.” Last June, he began to cross-post his daily “Today’s Polls” updates on “The Plank” in The New Republic. Rasmussen Reports also began to use the FiveThirtyEight.com poll averages for its own tracking of the 2008 state-by-state races.

Silver has been popular among baseball fans for several years after developing the PECOTA system (Player Empirical Comparison and Optimization Test Algorithm), which has been recognized by baseball analysts as being the most accurate system for forecasting how baseball players and teams will perform in the future.

At his blog, FiveThirtyEight.com, Silver examined trends in the 30 states that have voted on same-sex marriage bans and found they are becoming more difficult to pass every year.

Marriage bans, however, are losing ground at a rate of slightly less than 2 points per year. So, for example, we’d project that a state in which a marriage ban passed with 60 percent of the vote last year would only have 58 percent of its voters approve the ban this year. …

… So what does this mean for Iowa? 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.

The earliest Iowans would get a chance to vote on a constitutional amendment banning same-sex marriage would be late 2011.

Silver’s logic matches well with a recent poll conducted by the University of Iowa which found 60 percent of Iowans under age 30 support same-sex marriage, and three-fourths of Iowans under 30 favor some formal recognition of same-sex relationships. David Redlawsk, an associate professor of political science at the University of Iowa who oversaw the poll, said the figures show passion for banning same-sex marriage diminishing over time.

Silver predicts that by 2012, almost half of the 50 states would vote against a marriage ban, including several states that had previously voted to ban it.

Grassley has not had a truly difficult race in some time.  Some might argue he has not faced an evenly matched opponent since he defeated former Sen. John Culver in 1980.

In 2004, Art Small, a quirky, inexperienced, and virtually unknown Democratic challenger, lost to Grassley by about 40 percentage points.  But Small received no institutional support from the Democratic party, which essentially conceded the race before it began.

In 2010, the picture is very different.  While Grassley’s approval rating remains high, almost everything else has changed.

Democrats have begun to truly dominate Iowa’s political scene.  Majorities in both chambers of the state legislature are expanding, and a majority of Iowa’s congressmen are now Democrats.

Grassley has endeared himself to some liberal, good-government types with his work cracking down on the financial practices of megachurches, but that work has also earned him enemies on the right.

Most importantly, there is a big-name Democrat hanging around Iowa’s political scene with a dance card that is likely to remain empty for the next few years. What happens if former Gov. Tom Vilsack jumps into the race for Senate?

Fending off Vilsack’s challenge, Grassley could face deficits in both fundraising and name identification for the first time in decades.  Results from Grassley’s past elections would not reliably predict much of anything in that event.

Far from a ‘kamikaze mission,’ as Silver calls it, the emerging conventional wisdom around here is that Vilsack would have a real chance against Grassley in 2010.

The real question in my mind is, if Vilsack chooses to run and raises the $2 million he could probably raise for the campaign over the next year, does Grassley forge ahead, or does he bow out gracefully, giving away his seat?

The prediction came during his periodic series ranking the seats in the senate currently known to be contested in 2010. Grassley’s ranks 17 out of 35 contested races based solely on his age.

17. Iowa (R-Grassley)

Approval/Favorability Ratings: Chuck Grassley (R)
Poll               Date    Approve   Disapprove    Net
SurveyUSA          10/18     63          29        +34
Selzer             2/19      67          18        +49

This race ranks where it does solely because Grassley will be 77 in 2010 and could retire, in which case the race probably leans Democrat. Absent a retirement, a kamikaze mission by someone like Tom Vilsack against the popular incumbent is unlikely to succeed.

Silver points out that if those over the age of 65 did not vote, the measure would have failed.

At the end of the day, Prop 8’s passage was more a generational matter than a racial one. If nobody over the age of 65 had voted, Prop 8 would have failed by a point or two. It appears that the generational splits may be larger within minority communities than among whites, although the data on this is sketchy.

The good news for supporters of marriage equity is that — and there’s no polite way to put this — the older voters aren’t going to be around for all that much longer, and they’ll gradually be cycled out and replaced by younger voters who grew up in a more tolerant era. Everyone knew going in that Prop 8 was going to be a photo finish — California might be just progressive enough and 2008 might be just soon enough for the voters to affirm marriage equity. Or, it might fall just short, which is what happened. But two or four or six or eight years from now, it will get across the finish line.

This logic has implications here in Iowa, where the state Supreme Court is scheduled to hear arguments in the legal challenge to the state’s same-sex marriage law on Dec. 9. The topic of amending Iowa’s Constitution to ban same-sex marriage has been talked about for a number of years, but if the Court rules in favor of the plaintiffs, Republican outrage could be hard to ignore. In Iowa, amendments must be passed by the legislature in two separate sessions before being put on the ballot for a vote.

Unlike California, Iowa’s population is graying. Data from the U.S. Census Bureau shows that the Hawkeye State has a larger percentage residents older than 65 than does California, and that percentage is growing. By 2030, the number of Iowans 65 and older and those younger than 18 will be roughly the same.

If you go by Silver’s thesis, that an older population means a greater likelihood of a law similar to California’s Prop 8 passing, Iowa looks like fertile ground for those waging a battle against same-sex marriage to set up shop.

(h/t to John Deeth)