Marcum is a governance fellow at R Street Institute, a nonpartisan, pro-free-market, public policy research organization.

July's Democratic presidential debates highlighted a number of important national issues. From health care to economic inequality, candidates offered many purported solutions. The vast majority of these ambitious plans, however, face a fundamental constitutional roadblock: Congress.

Without congressional support, plans such as Medicare for All or amending the Immigration Nationality Act are dead on arrival. Voters, candidates and media alike are well aware that Senate Majority Leader Mitch McConnell would prevent any such legislation from passing his chamber, and if Republicans take the House, the chances for passage are even slimmer.

But if you were completely unfamiliar with American civics, you might have assumed from watching the debates that a president's role is to make policy and lambaste Congress when it does not comply. But of course, all legislative power rests with Congress. Viewers of the debates would be better served by questions that illuminate the presidency's actual institutional roles. These responsibilities are vital for governing, but we often fail to press candidates about them until it is too late.