In the 2008 Democratic primary, Barack Obama ran against an individual mandate for health care coverage, which his rival Hillary Clinton supported. But Obama then made it the cornerstone of the Affordable Care Act. Donald Trump campaigned on a mythical "tremendous" health care plan that would cost less, offer better care and provide more choices. George W. Bush ran on a "humbler" foreign policy.
The lesson here is not that candidates lie (that's a valid lesson, but one for another discussion). It's that things change, policy proposals don't make it through the legislative meat grinder intact, and quizzing candidates on the details of proposals that will never come to fruition is a waste of time.