With Donald J. Trump’s choice of Tom Price to head the Department of Health and Human Services, it’s clear that Republicans have a good chance of fulfilling their pledge to repeal Obamacare. In January, Republican majorities passed a measure similar to the one now proposed, which President Obama promptly vetoed. But with control of the presidency, they can prevail.

The prospect portends one of the biggest political backlashes in recent history. On Monday, a search of The New York Times archives since 1981 turned up 344 articles containing the phrase “Be careful what you wish for.” As the repeal effort gathers steam, expect that number to grow sharply.

Opponents of the Affordable Care Act have denounced it bitterly for more than six years, so it is not surprising that, despite the program’s successes, public opinion about it would be divided. Even so, a repeal would unleash the awesome power of loss aversion, among the more deeply rooted human tendencies known to behavioral scientists. Their consistent finding: The amount of effort people will expend to resist being stripped of something they already possess is significantly larger than the effort they will devote to acquiring something they don’t already have.

When the possession in question is an insignificant material object, such as a coffee mug, people must be offered roughly twice as much to part with it as they would have been willing to pay to acquire it initially. If the possession relates to health or safety, that ratio becomes drastically larger.