Brownback risked alienation of the apathetic majority, on the abortion issue, people who do not like “single issue” politicians.
Sorry, not buying it. A simple “no” vote without explanation or excuse would have been forgotten in a week, unless pro-choice zealots (do they exist in your worldview, or is it only those opposed to abortion who can be zealots?) chose to make an issue out of it, in which case their attack on Brownback would be the single-issue zealotry.