Harris and Trump Have Housing Plans. Economists Have Doubts.

America’s gaping shortage of affordable housing has rocketed to the top of voter worry lists and to the forefront of campaign promises, as both the Democratic nominee, Kamala Harris, and the Republican candidate, Donald J. Trump, promise to fix the problem if they are elected.

Their two visions of how to solve America’s affordable housing shortage have little in common, and Ms. Harris’s plan is far more detailed. But they do share one quality: Both have drawn skepticism from outside economists.

Ms. Harris is promising a cocktail of tax cuts meant to spur home construction — which several economists said could help create supply. But she is also floating a $25,000 benefit to help first-time buyers break into the market, which many economists worry could boost demand too much, pushing home prices even higher. And both sets of policies would need to pass in Congress, which would influence their design and feasibility.

Mr. Trump’s plan is garnering even more doubt. He pledges to deport undocumented immigrants, which could cut back temporarily on housing demand but would also most likely cut into the construction work force and eventually limit new housing supply. His other ideas include lowering interest rates, something that he has no direct control over and that is poised to happen anyway.

Economist misgivings about the housing market policy plans underline a somber reality. Few quick fixes are available for an affordable housing shortfall that has been more than 15 years in the making, one that is being worsened by demographic and societal trends. While ambitious promises may sound good in debates and television ads, actual policy attempts to fix the national housing shortfall are likely to prove messy and slow — even if they are sorely needed.

Here’s what the candidates are proposing, and what experts say about those plans.

Harris: Expand Supply Using Tax Credits.

Ms. Harris is promising to increase housing supply by expanding the Low-Income Housing Tax Credit, providing incentives for state and local investment in housing and creating a $40 billion tax credit to make affordable projects economically feasible for builders.