NutInShell is mostly right. Pay close attention to what they say about the law when you ask. The wording matters. There's 6 answers: will vote, will probably vote, is leaning towards, is leaning against, will probably vote against, and will vote against. The most extreme ones have no ambiguity. They will vote that way. If they say they will probably vote then you can stop swaying them at that time as they should vote that way most times. So concentrate on swaying those that are leaning.
Note that with enough time you can sway someone that says "will vote against it" to change it to "will probably vote against it". But I would take a lot.