Then remember the three percent plus one voter margin, and double your efforts to mobilize. Before long, even this politician will go to a new tactic. Rome was not built in a day, nor is major policy passed overnight. Sometimes it may take years. Second of all, the reason this is often true is that politicians succeed in ducking difficult votes, thus preventing voters from ever knowing exactly where they stand.
Private promises are worthless.
When you have insisted on the politician's support for your position, they will then try to buy you off. Here is where most grassroots leaders fail. Power and Influence and Selling Out Politics can be seductive. These are the trinkets for which leaders sell our their political agenda. Of course, most everyone thinks he is strong enough, smart enough, and committed enough not to sell out.