When is it ok for a lawmaker to vote against the will of a majority of his or her constituents?

Last year, in Aitkin in north-central Minnesota, a solid majority of people voted for a proposed constitutional amendment defining marriage as between one man and one woman, effectively banning same-sex marriages. Even so, the first-term representative from the area says he will vote for the bill to legalize same-sex marriage.

His constituents are not happy.

Today’s Question: When is it ok for a lawmaker to vote against the will of a majority of his or her constituents?