Sen. Byron Dorgan, D-N.D., walks out of his office on Capitol Hill on January 6, 2010 in Washington,
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Dorgan on the Hill today.

Sen. Byron Dorgan, D-N.D., walks out of his office on Capitol Hill on January 6, 2010 in Washington,
Mark Wilson/Getty Images

Dorgan on the Hill today.

Why is Sen. Byron Dorgan, D-N.D., planning to leave the Senate at the end of this year?

He just told All Things Considered co-host Michele Norris that a major reason is that after 40 years in public office, he'd like to do some other things — such as write a few more books.

Here's some of what he had to say:

Dorgan also told Michele he thinks he could have won re-election, even against popular Republican Gov. John Hoeven. And he said he didn't know that his announcement would come within 24 hours of word from fellow Democrats Sen. Chris Dodd of Connecticut and Gov. Bill Ritter of Colorado that they too won't seek re-election.

Much more from their conversation is due on today's edition of ATC. Click here to find an NPR station near you that broadcasts the show. Later, the show's piece will be posted here.