President Joe Biden said his administration has "to do better" to meet COVID-19 testing demands.

During the White House COVID-19 Response Team’s call with the National Governors Association Monday, the president directly addressed the shortages of kits being reported across the nation.

He said the steps the government had taken so far to make more COVID tests available is "not enough."

"If I had known, we would have gone harder, quicker if we could have," Biden said on the call.

He went on, "Seeing how tough it was for some folks to get a test this weekend shows we have more work to do and we’re doing it. We have to do more, we have to do better, and we will."

Dr. Anthony Fauci said a COVID vaccine requirement for domestic air travel should be "seriously" considered.

"If you're talking about requiring vaccination to get on a plane domestically, that is just another one of the requirements that I think is reasonable to consider," he said Monday on MSNBC's "Morning Joe."

"When you make vaccination a requirement, that's another incentive to get more people vaccinated. If you want to do that with domestic flights, I think that's something that seriously should be considered," he said.

This is not the first time that Fauci has argued for vaccine mandates domestic flights.

On Sunday, Fauci told ABC's Jon Karl that "anything that could get people more vaccinated would be welcome."

-ABC News' Arielle Mitropoulos

Mayor Bill de Blasio said New York City has administered more than 180,000 COVID vaccine booster shots since a $100 incentive was announced on Tuesday.

This brings the total number of residents who have received boosters to more than 1.9 million.

"We did a booster incentive and it has been heard and felt by the people of NYC," de Blasio told MSNBC on Monday.

-ABC News' Aaron Katersky

At least four U.S. cruise ships are reporting COVID-19 outbreaks aboard, leading to them being denied entry to -- or turned away from -- foreign ports.

Holland America's Line Koningsdam was denied entry into Puerto Vallarta on Thursday after 21 crew members tested positive.

Additionally, the Carnival Freedom ship was turned away from the Caribbean Islands of Bonaire and Aruba on Wednesday and Thursday, respectively, after "a small number" of passengers aboard tested positive for the virus.

Officials in Aruba and Curacao also turned away Royal Caribbean's Odyssey of the Seas on Wednesday after 55 fully vaccinated crew members and passengers tested positive.

On the same day, passengers aboard the Seven Seas Mariner were not allowed to disembark in Cartagena, Colombia, after six crew members and one passenger tested positive for COVID-19.

The U.S. recorded more than 486,000 new COVID-19 cases in a day, marking the third straight day of record numbers, according to data released by the U.S. Centers for Disease Control and Prevention.

The new data comes as states are going through their huge backlogs of tests taken during the Christmas weekend.

In the last week, the U.S. has reported more than 2.2 million new cases, which averages out to about 220 Americans testing positive for COVID-19 every minute.

The CDC will not be providing new data updates until Jan. 3, due to the New Year's holiday.

-ABC News' Arielle Mitropoulos