Mr. Paul, in his response, wrote that he was willing to engage because he was seeking “to restore our constitutional system of separation of powers” after a decade of “unconstitutional claims of authority by the president.” (Back in 2011, after Mr. Obama authorized the bombing of Libya without congressional authorization, Mr. Paul denounced the move in a Senate speech while standing before a poster of a quote from Mr. Obama’s 2007 answers to my survey. Mr. Obama said then that the Constitution did not give presidents the power to do such a thing.)

But none of the other campaigns chose to answer the questions. Mrs. Clinton’s campaign did provide a general statement in which she expressed pride in helping the Obama team turn the corner on certain Bush administration detainee policies. She added that while she would fight terrorism “vigorously,” she would only appoint officials and adopt policies that protected human rights and were “faithful to the law.”

But when it comes to executive power, people often disagree about what it means to be faithful to “the law.” So why are the candidates so less willing this time to tell voters what they think?

The dynamics may be different for each party. Among Republicans, possible explanations include not wanting to acknowledge expansive views of executive power at a time when conservatives are portraying Mr. Obama as imperial, or to identify limits they might later exceed.

“Maybe this is the Obama lesson,” said Harold Bruff, a University of Colorado constitutional law professor. “ ‘I don’t want to say anything because someone will make hay of it.’ ”

Still, those factors existed four years ago, too. What seems to have changed is the Republican electorate’s attitude. The establishment candidates like Mr. Bush have advisers who worked in previous Republican administrations and could draft answers based on their experience. But Mr. Trump’s wild-card campaign is overshadowing those candidates. If expertise does not matter to primary voters, what’s the point of tackling hard questions?

“The front-runner has shown he doesn’t have to get into the weeds, so there is no percentage of doing it for the rest,” said Bruce Buchanan, a political-science professor at the University of Texas at Austin. “Why get specific and give someone a target to criticize?”