It's subject to local zoning laws and varies too much across markets to have federal-level arguments about the topic, the thinking goes. Even after the mortgage market tanked the economy , candidates rarely talked about housing as something they had that much power to influence.

That's changing in 2020 — in a big way.

The Democratic presidential field is littered with proposals to ease the affordability crunch plaguing America's most prosperous cities. A bill offered by Sen. Kamala Harris would create refundable tax credits for anyone making less than $100,000 and paying more than 30% of their income in rent, while Sen. Cory Booker would tie federal community development grants to more relaxed zoning regulations.

Rapidly escalating rents are even melting a decades-long aversion to having government itself build public housing, rather than incentivizing developers through convoluted tax breaks . Sen. Elizabeth Warren's plan, for example, would distribute $450 billion to states over 10 years with the goal of building or preserving 3.2 million affordable housing units.

Missing in much of the debate, however, is context on the scale of the affordability problem, who faces the worst of it, and what kinds of needs are expected to crop up in the future.

For more than 30 years now, Harvard's Joint Center for Housing Studies has put out a comprehensive report on those questions. Their latest edition , released Tuesday, finds that while the squeeze on renters actually eased slightly in 2018, the United States is still producing far fewer housing units than are needed to meet demand.

Here's the reality of the housing market in America in 2019:

Construction slowed down in 2018 after a couple productive years in 2016 and 2017. America needs about 1.5 million new housing units per year, or about 260,000 higher than in 2018, the Joint Center estimates.

The Joint Center predicts there will be 400,000 new renters per year going forward. That's after the total number of renters declined for two straight years as household balance sheets finally improved enough to allow people to buy homes.

The share of people who spend more than 30% of their income on housing has decreased overall since its peak in 2010. That decline has mostly come among homeowners, in part as a result of low mortgage interest rates and strong income gains. Renters continue to bear a high cost burden, with 47.4% paying more than 30% of their income on housing. The number of units priced lower than $800 per month has shrunk by more than 4 million since 2011, in inflation-adjusted terms.

Home prices are still rising, but at a slower pace. But that doesn't mean housing is cheap. Adjusted for inflation, housing prices are now only 7.6% below their housing-bubble high.

But that doesn't mean housing is cheap. Adjusted for inflation, housing prices are now only 7.6% below their housing-bubble high. Millennials are starting to get married and wanting to buy homes, but they have lower incomes and higher debts than their parents did as young people. And the housing market isn't producing enough smaller, lower-priced homes to start them out in. Homes under 1,800 square feet made up only 22% of the new housing stock — 10 percentage points less than two decades ago — and construction of multifamily condos has been moribund since the recession.

The population experiencing homelessness decreased by 87,000 from 2008 to 2018, in part because of public commitments to policies that house people first without pre-conditions related to substance abuse or job training. But the homelessness rate started to tick up again in 2018, driven by unsheltered homelessness, or people living on the street rather than with friends or relatives or in shelters. The problem is particularly bad in West Coast cities; the number of unsheltered homeless people grew 25% in California from 2014 to 2018, to 89,500.

There are fewer people living below the poverty line now than there were during the recession, but that figure is still 35% above where it was in 2000, according to the Census Bureau. Poverty has also become more concentrated in certain neighborhoods.

The most difficult obstacles to housing construction are the availability of labor and the cost of land in urban areas close to jobs. Over many decades, the federal government has retreated from its role providing a safety net for people whose incomes aren't keeping up with the cost of housing. As a stopgap, some jurisdictions have even gone back to rent control, which keeps rents from escalating quickly but is also unpopular with economists because it may constrain new housing production down the line.

Chris Herbert, managing director of Harvard's Joint Center for Housing Studies, sees such measures as a symptom of broader policy failure.

"The fact that we're turning to rent control is a sign that we've failed at other direct ways of addressing these issues," Herbert said. "We're not providing enough direct subsidy to people who need it."

Ultimately, Herbert thinks, the private market will have to step up and deliver the kinds of housing units that people want and can afford, rather than simply building for the high-end luxury market, which has been the case for much of the post-recession era. And companies can only do that if local governments allow them to build more densely. But, he says, proposals for the government to play housing developer again may be a valuable part of the mix.

"There's a segment of the country that does not make enough money to pay rents that will support privately provided housing," Herbert said. "Government programs don't have to be distortionary if done right. I think we ought to be open to different ways of doing things and not dismiss public housing as a failed model."