Although Nate Silver’s status as a political forecaster was cemented by this year’s presidential election, I take issue with his suggestion that Sen. Chuck Grassley is a lock to retain his seat in 2010.  Briefly, here’s why:

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?