The public may buy or dismiss campaign promises like Donald Trump's to build a wall on our southern border and have Mexico pay for it or Bernie Sanders' plan to provide single-payer health care and tax the rich to pay for it. But while some may be dubious of those promises, at least they are being made publicly, giving voters the opportunity to weigh their merits.

But many of the promises that candidates for office at all levels of government are making are secret -- promises to interest groups that the public has no way of evaluating.

Those promises are happening in the behind-the-scenes process of interest-group questionnaires. Anyone who campaigns for office soon realizes that interest groups usually require candidates who are seeking endorsements to answer these surveys. Organizations from unions to advocacy groups to professional societies use them.

In concept, these candidate questionnaires may seem perfectly reasonable, as groups want to ensure that the candidate's interests are aligned with theirs before bestowing their support. However, too often candidates' responses are kept confidential, supposedly to allow the candidate to feel more comfortable answering.

The secrecy is a problem for a number of reasons. First, it's an invitation to dishonesty. When a campaign really needs an endorsement, secret responses provide the temptation to answer one way for one group of endorsers and differently for another group.

Another problem is that candidates are in essence creating secret obligations on matters about which voters have a right to know. If an environmental group knows how a candidate intends to vote on a bill mandating greater use of renewable energy, for example, shouldn't the voters also know? And why should a Chamber of Commerce know how a candidate promises to vote on a transportation issue when voters do not?

Finally, these questionnaires create the impression that candidates have already made important decisions on public-policy matters before they have had a chance to hear both sides through public hearings and deliberation with their peers. If candidates are pre-committed to certain positions through their interactions with interest groups, they aren't really going into the process of governing with an open mind.

Not everyone sees the current process as problematic. Marc Paul, former deputy editorial page editor of the Sacramento Bee, argues that nothing in politics is truly secret. "Perhaps 23 years of hearing candidates say one thing in endorsement interviews, then do the opposite, has made me cynical," Paul wrote, "but candidate pledges deserve about the same weight as a teenage boy's answer to the question, 'Will you respect me in the morning?'"

Perhaps, but if this argument is correct, why not just make all of the questionnaires public? If an endorsing group does not want their questions and the candidate's responses to be made known, question the endorser's motives. Are they creating an obligation that they know voters won't like but that can be used against the candidate later once he or she takes office? That kind of endorsement will certainly prove more trouble down the road than it is worth.

And before candidates answer interest groups' secret questionnaires, they should ask themselves if the promises made in those documents would effectively tie their hands and prevent them from participating fully in the deliberative process. Open and honest governance needs all the help it can get.