Is a Japan transit visa required for a 19-hour layover at Haneda?

Yes, you can transit without a visa at Haneda airport, if your connection time between flights is less than 72 hours.

If you have not been to any of the areas affected by Covid-19 then you may also be able to get a Shore Pass so that you can enter Japan and stay landside during your layover.

Timatic, the database which airlines use to verify passenger travel documents, states in part:

Visa required, except for Passengers transiting through Tokyo (HND) or Osaka (KIX) with a confirmed onward ticket for a flight to a third country within 72 hours. They must stay in the international transit area of the airport and have documents required for the next destination.

Visa required, except for Passengers with a passport and a confirmed onward ticket to a third country within 72 hours can obtain a Shore Pass on arrival if there are no connecting flights on the same calendar day. They must:

• have documents required for the next destination; and

• have proof of sufficient funds to cover their stay; and

• arrive at and depart from an airport or seaport located within the same group below.

• Group A:
  Airports: Narita (NRT), Haneda (HND), Nagoya (NGO), Niigata (KIJ), Komatsu (KMQ) and Yokota (OKO). Seaports: Tokyo, Yokohama, Niigata and Nagoya.

(Covid-19 entry restrictions omitted as these change frequently. At this time I don't recommend trying to get a Shore Pass as people entering Japan from the USA are being asked to self-quarantine for 14 days.)

The Government of Japan will be extending its entry ban to the U.S.; any foreign citizen except for permanent residents will be refused entry if they have traveled to the U.S. in the past 14 days. The ban will likely be in effect in just a few days, so there's a very good chance that you won't be able to make the transit.

If you stay airside, I am not sure, but I strongly suspect that you will still be refused boarding.

Per Michael Hampton's answer, you can transit airside at Haneda for up to 72 hours without a visa.

Furthermore, the current Covid-19 entry restrictions only affect entry, not transit.

As such, if your trip is in a single booking, you're OK.

From TIMATIC:

Visa required, except for Passengers transiting through Tokyo (HND) or Osaka (KIX) with a confirmed onward ticket for a flight to a third country within 72 hours. They must stay in the international transit area of the airport and have documents required for the next destination.

and

Passengers who have been in Andorra, Austria, Belgium, Denmark, Estonia, France, Germany, Iceland, Iran, Ireland (Rep.), Italy, Liechtenstein, Luxembourg, Malta, Monaco, Netherlands, Norway, Portugal, San Marino, Slovenia, Spain, Sweden, Switzerland or Vatican City (Holy See) in the past 14 days are not allowed to enter Japan.

(they haven't added the US yet)