Donald Trump dismissed criticism from the media and Republican rival Ron DeSantis after Trump "mixed up" Barack Obama and Joe Biden.
In some recent campaign speeches, Trump appeared to confuse Biden with his former boss.
Trump said that he was being "sarcastic" and alluding to Obama's rumored influence over the Biden administration.
DeSantis has presented himself as a fresh alternative to 77-year-old Trump, whom DeSantis has increasingly likened to 80-year-old Joe Biden.
The DeSantis campaign launched a "Trump accident tracker," and last week DeSantis told CNN that "Father Time" has worn Trump down, leaving him "wedded to the teleprompter."
“Look, when you get to this point — the presidency is not a job for somebody that’s pushing 80 years old, I just think that that’s something that has been shown with Joe Biden,” DeSantis said. "Father Time is undefeated. Donald Trump is not exempt from any of that.”
DeSantis has also criticized Trump for skipping the primary debates, which Trump has called a distraction and waste of time given his dominant lead.
So far, DeSantis' attacks don't seem to have landed as primary voters flock to the former president, leaving DeSantis struggling to close the gap.
In his Monday post, Trump asserted that he took a cognitive test and "ACED IT," challenging Biden to take one as well.
Trump also said that "DeSanctimonious" and the media are both peddling a disingenuous narrative about Trump's cognitive health.
"Whenever I sarcastically insert the name Obama for Biden as an indication that others may actually be having a very big influence in running our Country, Ron DeSanctimonious and his failing campaign apparatus, together with the Democrat's Radical Left 'Disinformation Machine,' go wild saying that 'Trump doesn't know the name of our President, (CROOKED!) Joe Biden," Trump wrote.
"He must be cognitively impaired.' No, I know both names very well, never mix them up, and know that they are destroying our Country," he added.
Trump is just a few years younger than Biden, but the widespread concern that voters have about Biden's age does not extend to Trump in most polls.
In fact, Trump is edging out Biden in the latest polls, leading Democrats to fear that Biden's re-election is in jeopardy.