Former President Donald Trump has mixed up former President Barack Obama with President Joe Biden again. Trump's gaffes fueled concern over his age as the election campaign against his possible opponent, also advanced in age, picks up.

Donald Trump Confuses Barack Obama Obama for Biden

During a rally in Richmond, Virginia, on Saturday night, Donald Trump was discussing Vladimir Putin when he said the Russian president "has so little respect for Obama that he's starting to throw around the nuclear word," The Guardian reported.

"You heard that. Nuclear. He's starting to talk nuclear weapons today," Trump added.

The crowd reportedly went silent after the 77-year-old former president's reference to Barack Obama before he named Joe Biden and called him "a fool." 

It was the eighth time Trump had confused Biden with Obama in recent months, with one of the most recent happening in November when recounting a speech by Hungarian Prime Minister Viktor Orban, Forbes reported.

Next was during an October 1 rally in Iowa, twice during a Fox News Radio interview on October 11, and then three more times during a speech to faith leaders in Washington last September 15.

The former president has been prone to similar gaffes, including confusing Republican rival Nikki Haley with former House speaker Nancy Pelosi. Haley, who is framing herself as a younger option, has underscored Trump and Biden's age in her campaign ads, labeling them as "Grumpy Old Men."

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Gaffes of Joe Biden and Donald Trump Become a Concern For Voters

Donald Trump's blunder came a day after Joe Biden twice confused Ukraine with Gaza while discussing the US airdropping humanitarian supplies to Palestinians in Gaza.

"In the coming days, we're going to join with our friends in Jordan and others who are providing airdrops of additional food and supplies into Ukraine," the 81-year-old president said on Friday. Biden added that the US will "seek to open up other avenues into Ukraine, including possibly a marine corridor." 

The confusion prompted a clarification from a White House official, who corrected Biden's remarks, saying that the president meant Gaza, not Ukraine. Because of these gaffes, Biden and Trump's age and mental well-being remain a concern for voters.

According to a new New York Times/Siena College poll released on Sunday, 42% say they at least somewhat agree that Trump is too old to be an effective president, while 73% said the same about Biden.

READ MORE: Joe Biden's Gaffes Becoming More Frequent: Meeting With Dead French Leader Just the Latest Instance of His Confusion