Most rational minds would agree with you. But it's not rational thinking that convinces plains voters to look to the Republicans or worse - to the rabid hateful-right wilderness of the Republican party.

For an excellent primer on plains politics, read "What's the Matter with Kansas? How Conservatives Won the Heart of America", by Thomas Frank. It's funny and illuminating and very very alarming for those of us who have assumed that we could win over our fellow Americans with a common sense argument that focuses on jobs, health care, education, the environment and a decent overall quality of life.

After reading Frank's book, it's clear to me that we have decades of hard work ahead of us undoing the damage done by a quarter century of hate-filled right-wing propaganda that has effectively moved a large swath of America's heartland into the deep red for the foreseeable future.

What I am most interested in would be the percent of the population that is Native America.  Population growth has all but stagnated in most of the Great Plains.  It ranges from negative growth to a slow crawl.  But the big story is how the young white population, which is amazingly well educated, continues to flee the states.  The people stuck in the states for the long term tend to be Native Americans and there is a strong chance for Democrats to appeal to them.  I'm not sure if we'll ever be able to form a majority in these states, but it's worth considering.

as I understand it, the Plains states are experiencing rural flight -- people moving from rural counties to the cities. I'm not sure if the people would make the cities more conservative or if the cities would influence people and make them more liberal.

Population growth is actually happening in the suburbs and rural areas.

Minnesota - http://www.epodunk.com/top10/countyPop/c oPop24.html

The political history of the Great Plains is truly fascinating stuff.  Lest anyone forget, about 100 years ago the area was a hotbed of progressive activism.  Small farmers formed unions to counteract the influences of Eastern big business.  New poiltical parties, the Greenbacks, People's, Populists and Non-Partisan League, won state and federal elections from Colorado to Texas to North Dakota and fought on the side of the working farmers against capitalists.  Nebraska was home to the fiery William Jennings Bryan, who (arguably) gave birth to the modern Democratic Party platform.  Eugene V. Debs also found some of his most receptive audiences in that state.

This movements faded by the 20's and have been truly extinct ever since 1964, the last time a Democratic President carried these states.  Most of the last of the old guard Senators representing the earlier movements were swept out in 1980 (Birch Bay of IN, Frank Church of ID, Geroge McGovern of SD).

One single issue probably cannot explain the shift, and its probably more complicated than Frank's concept of liberal elitism and social immorality alienating the heartland crowd.  As you pointed out, very many people have left these places, and thus family farms have largely been replaced by huge factory farms run by corporations.  Republicans in congress, however fiscally conservative they may claim to be, give plains farmers plenty of farm subsidies.
I have spent a little (but not much) time in this part of the country.  The issues you bring up (sustainablility, etc.) are good ones for Dems to run on.

To some extent, they have already worked.  North Dakota has been overwhelmingly electing two populist senators for the past 15 years (so was SD until 04), and Democrats have recently been very sucessful governing Kansas, Oklahoma, and Wyoming.

If we ever want to win these places at the national level, it would be a good idea to NOT have John Kerry at the top of the ticket.  Another good idea might be actually campaigning there.  Of course this would waste money and time during the first few presidential elections, but it would at least begin to deliver the messsage to heartland voters that we DO acknowledge them and care about their well-being. On the long term I believe this strategy would pay off.