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- Joe Biden is facing pressure to take a cognitive test after debate stumbles and verbal errors.
- Biden said he won't take one, adding in an interview: "I have a cognitive test every single day."
- Experts cautioned that a cognitive test could set a dangerous precedent for future campaigns.
Joe Biden is facing mounting pressure to prove he's medically fit to run for a second term, but experts say a cognitive test could set a dangerous precedent.
Biden stumbled through his first presidential debate of the year against former president Donald Trump on June 27.
The 81-year-old president made verbal errors and appeared to lose his train of thought on several occasions.