President Biden misspoke in a speech Thursday offering updates on an update on vaccination progress in the U.S., referring to his vice president as "President Harris." 

"When President Harris and I took ..." Biden said, before momentarily pausing, "a virtual tour of a vaccination site in Arizona not long ago, one of the nurses on that tour injecting people, giving vax each shot, was like administering a dose of hope." 

At the same time, the president announced the administration would achieve its goal of 100 million vaccines administered in 100 days on Friday, the 58th day of the new administration. At this point, Biden said, 65% of people aged 65 and older have received at least one dose of a Covid-19 vaccine.

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The president has made such gaffes before. In December he mistakenly referred to Harris as "president-elect," also during a speech on Covid-19 vaccines. "I took it to instill public confidence in the vaccine. President-elect Harris took hers today for the same reason," Biden said. 

The comments ignited speculation of cognitive decline from the right, following a campaign where Biden repeatedly appeared tongue-tied. 

Harris, too, once accidentally dubbed herself commander-in-chief. "A Harris administration, together with Joe Biden as the president of the United States," she said at a virtual roundtable in September. 

"The Biden-Harris administration will provide access to $100 billion in low-interest loans and investments from minority business owners," she continued.

In a Democratic debate in July 2019, Biden called his opponent Sen. Corey Booker, D-N.J.,  the president.

While criticizing Booker's criminal justice plan, he said: "The fact is that the bills that the president, excuse me, the future president, that the senator is talking about, are bills that were passed years ago and they were passed overwhelmingly."

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Booker quipped, "Well first of all, I’m grateful that he endorsed my presidency already."