Renters are less able to pay rent than before the coronavirus pandemic, but that isn't the only factor now bedeviling apartment landlords.

Evictions are difficult or impossible for now, banks are less willing to finance multifamily deals and rents — even those that are being paid — are dropping.

Nearly a fifth of all U.S. apartment renters (18%), or more than 10 million households, are behind on rent, according to the most recent Household Pulse survey from the U.S. Census Bureau. On average, the renter who is behind at all is behind by $5,600 on rent, or about four months' worth, CNBC reports, citing data by Moody's Analytics and the Urban Institute.

Altogether, that means Americans owe a total of $57.3B to their landlords, large and small, as of January. In New York City alone, tenants owe an estimated $1B in back rent.

The December stimulus bill provided $25B in rent relief, and President Joe Biden's proposal for another stimulus would provide another $25B, but its fate in Congress is uncertain.

In California, Gov. Gavin Newsom and legislative leaders proposed that the state would pay 80% of most people's unpaid rent, provided landlords agreed to forgive the 20% balance, NBC reports. Though the California Apartment Association, which represents multifamily landlords in that state, wasn't entirely happy with that approach, the organization is pressing for money to help its members.

“Without this money, many landlords are at risk of losing their rental units," CAA Executive Vice President Debra Carlton told NBC.

For now, eviction for nonpayment of rent isn't an option for landlords, since one of the first acts of the Biden administration was to extend the federal eviction moratorium through the end of March. The federal moratorium, as well as various state and local actions before that, have prevented at least 1.6 million eviction filings nationwide, Eviction Lab estimates.

Banks are warier of the multifamily industry as well. At the beginning of the pandemic, about 4.6% of apartment debt held by banks was considered high risk, The Wall Street Journal reports, citing Trepp data. As of December, that total was 16.9%.

"A lot of this was driven by people being in stress,” Trepp Vice President Russell Hughes told the WSJ.

As landlords asked for forbearance from banks, the perception of risk for apartment industry loans rose.

Investors are also now more skeptical of the apartment sector as an investment class, with large public owners seeing their share prices slide. As of Tuesday, Equity Residential's per-share price has dropped from $82.34 a year ago to $62.63, Avalon Bay fell from $218.86 to $168.11, and UDR is down from $48.05 to $39.21.

A longer-term challenge for apartment landlords is declining rents. In 2020, according to RENTCafé, apartment rents decreased in each of the 10 most expensive cities as the number of renters declined. In the most expensive market in the country, San Francisco, rents were down 17.3% year-over-year, but even in relatively less expensive places such as Austin, Texas, and Portland, Oregon, rents dropped 4.9% and 3.2%, respectively.