A few years ago, Al Franken wrote a “satire on the breakdown of civility in public discourse.” He called it, Rush Limbaugh Is a Big Fat Idiot. Franken’s point was that Limbaugh became popular by polarizing people. Franken made that point by writing as polarizing a book as possible.
We see this polarization in the current presidential campaign. Obama has become popular because he promises a way out of the polarization. Hillary’s response is to polarize Democratic voters against Obama, and it seems to have worked: two weeks ago, polls showed that Hillary supporters would vote for Obama if he became the nominee; after the Texas-Ohio primaries, polls showed her supporters to be more hostile of him.