Philadelphia, Pennsylvania - President Joe Biden suffered an embarrassing slip-up during an interview as concern over his fitness for re-election continues.

In a conversation with the radio station WURD in Philadelphia, which is aimed primarily at a Black audience, the president struggled to find the right words.

Biden wanted to describe the fact that he had served as Vice President to former President Barack Obama and then later chose Kamala Harris as his own running mate.

In doing so, however, he floundered and instead said: "By the way, I'm proud to be, as I said, the first vice president, first Black woman, to serve with a Black president."

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This wasn't the only slip, however.

At another point, Biden said, "I'm the first president that got elected statewide in the state of Delaware when I was a kid."

The interview was intended to reassure voters after the failed TV debate and convince them that Biden was still capable of holding office, but the attempt has evidently backfired.

Biden is set to participate in a high-stakes interview with ABC's George Stephanopoulos on Friday night as the campaign attempts to right the ship following the debate disaster.