Harris visited a pharmacy in a Giant supermarket in a predominantly minority neighborhood of Washington, D.C., on Thursday in an effort to ease vaccine hesitancy on the same day she and Biden will tout reaching the 50 million-shot marker, which is halfway to their 100 million shots in 100 days goal. But on the same day of Harris' visit, there were problems with the district's website to register for vaccine appointments.

D.C. Mayor Muriel Bowser said the website issues were caused by a crush of demand after eligibility was expanded to include people with pre-existing conditions like severe obesity, asthma, liver disease and other conditions.

At the event, Harris spoke to Brenda Thompson, a D.C. resident who was about to receive her second dose, about her experience getting the Moderna vaccine, with Harris saying she needed to "take it a little slow" the day after her second dose.

Harris spoke with the store's pharmacist, Samir Balile, who told Harris he sees lines of people every day waiting for their shots, but he is concerned about hesitancy in the coming weeks.

Harris reported to him feeling some side effects after the second dose.

"The first dose, I was fine. The second dose, I thought I was fine, got up early in the morning, went to work, then midday I realized I might need to slow down a bit. Just that one day, and then it was fine, it was like nothing," Harris said.

-ABC News' Sarah Kolinovsky and John Parkinson

Biden and Harris will participate in an event Thursday afternoon commemorating 50 million COVID-19 vaccine shots administered during the Biden administration, which is halfway to Biden’s goal of distributing 100 million COVID-19 shots in his first 100 days in office.

When Biden set out the goal at the beginning of his term, the administration was already on pace to administer nearly 1 million vaccines a day, which some public health experts have said is not fast enough to control the pandemic.

Dr. Anthony Fauci, Biden’s chief medical adviser, has estimated that 325 million people will need to be immunized for the pandemic to end and to reach that threshold, Biden would need more vaccinations.

Biden has rejected the suggestion that his goal was too low, telling reporters in January that, "it's a good start."

Meanwhile, Harris visited a Giant supermarket in Southeast Washington, D.C. Thursday morning to promote the administration’s Federal Retail Pharmacy Program for COVID-19 vaccinations, which has delivered 1 million doses to over 6,500 pharmacies across the country.

Harris spoke to the store's pharmacist and then watched as a patient, Brenda Thompson, received her second dose of the Moderna vaccine.

Biden will also participate in the National Governors Association’s Winter Meeting Wednesday afternoon, and the White House will give a press briefing at 12:30 p.m.

-ABC News' Molly Nagle, Anne Flaherty and Stephanie Ebbs

Biden issued a major disaster declaration for Oklahoma in the wake of winter storms in the U.S. south. The declaration covers 16 counties in Oklahoma and allows increased federal funding for recovery.

On Saturday, Biden issued a major disaster declaration for Texas, which freed up funds to aid recovery efforts after the storms left millions without power. The president is set to visit Texas on Friday to see relief efforts and visit a vaccine distribution facility.

-ABC News' Sarah Kolinovsky

The Republican Party is both less divided and more divided than it seems at the moment -- and not in ways that glide along the easiest political paths.

On the question of former President Donald Trump, the GOP is less divided than a colorful House leadership news conference might make it seem. The party still belongs primarily to Trump, as the CPAC gathering that begins Thursday in Florida will demonstrate.

On the question of President Joe Biden's agenda, there's actually more GOP dissension than meets the eye. The first floor votes on Biden's COVID-19 package are coming Friday in the House, yet united Republican opposition in Congress doesn't align with public polling on the topic.

Among the public at large, Biden and his COVID plans are considerably more popular than Trump and opposing COVID relief, at least for now. But Republican lawmakers appear to fear more political blowback in opposing Trump than voting "no" on COVID bills.

-ABC News Political Director Rick Klein