TOPEKA, Kan. — Four years ago, Joan Wagnon was a 70-year-old grandmother preparing to retire after decades of public service. A centrist Democrat long credited as blazing the way for women in politics in Kansas, she spent 12 years in the state Legislature and four years as mayor of Topeka — the first and only woman to hold the job. After eight years as state secretary of revenue, Wagnon was preparing to hang it up when "the massacre" happened. On Election Day 2010, Sam Brownback, a two-term, hard-line conservative U.S. senator and a 2008 candidate for the Republican presidential nomination,...