Writing in The Week, Joel Mathis stated the problem well:
The democratic process starts at the local level. There are many little-known and ill-paid elected local officials whose motivations have little to do with ideology or ambition. They simply have a desire for public service. Very few of these people get rich or powerful on the school board, but they do give a lot of time and energy to serve. Attempts to intimidate them in their work or scare them away from pursuing office altogether erode American democracy at a fundamental level.
Community by community, American democracy works in large part because countless thousands of our fellow citizens choose to dedicate immense amounts of time at relatively low levels of pay (or sometimes for no pay at all) to serve at the lowest levels of governments. They should not be immune from critique. Every person who enters public service should be prepared to face the public.
But there is a vast difference between vigorous debate and outright harassment, much less threats of violence. If that is perceived to be the price of admission into public office, we will see a diminishing number of responsible citizens choose to subject themselves or their families to relentless abuse.