Hillary Clinton and the Clinton Foundation: what's the dividing line?

The Clinton Foundation's raised more than $2 billion since 2001. Among other good works, it's widely praised for helping to prevent or control outbreaks of HIV. Potential conflicts of interest between Hillary Clinton and the Foundation were raised during her confirmation hearings as Secretary of State. Now, they're a major issue in her campaign for the White House. This week, the Associated Press reported, "More than half the people outside the government who met with Clinton while she was secretary of state gave money either personally or through companies or groups, to the Foundation." Donald Trump says that's evidence that contributions were the price of access. Do such contributions reveal a smoking gun? Could Clinton have avoided the scandal before it ever began?