Former Vice President Joe Biden made another gaffe on Tuesday, this time suggesting that his child tax credit plan will put "720 million women" back into the workforce.

Speaking at the Workers’ Presidential Summit in Philadelphia, the 2020 frontrunner mocked the idea of having a tax break for "a racehorse" and not one for having children.

"You get a tax break for a racehorse, why in God's name couldn't we provide an $8,000 tax credit for everybody who has childcare costs?" Biden told the crowd. "It would put 720 million women back in the workforce. It would increase the GDP, to sound like a wonk here, by about eight-tenths of one percent. It would grow the economy."

According to the U.S. Census, there are 330 million people living in the country.

BIDEN'S GAFFES, STUMBLES, AND FITNESS TO LEAD FOR OFFICE UNDER FIRE IN NEW TRUMP CAMPAIGN VIDEO

Biden's gaffes have recently been targeted by the Trump campaign in a new video questioning his fitness to lead.

The web video, tweeted Tuesday morning by campaign manager Brad Parscale and shared first with Fox News, stitches together everything from his recent debate-stage musing about "record players" to his statement that "poor kids" are just as talented as "white kids." Interspersed with the clips of the 76-year-old Biden's comments are those of pundits wondering about his stumbles, shakiness, mental and physical stamina, whether he’s “lost a step” and whether he’s “equipped for a very grueling campaign.”

The former vice president’s age and mental acuity have been questioned ever since he launched his 2020 presidential campaign in late April. Last week, the front-runner in the Democratic nomination race faced repeated attacks from rivals over his memory.

Former Housing Secretary Julian Castro, who served in the Obama administration with Biden, landed arguably the lowest blow when he swiped at Biden’s memory -- accusing him of contradicting himself on whether Americans would have to buy into his health care plan.

"You just said two minutes ago they would have to buy in. Are you forgetting what you said two minutes ago?" Castro asked, in what appeared to be a reference to past senior moments by Biden.

In that case, as the Biden campaign later noted, Castro was wrong. Biden did not say during the debate that individuals would have to buy in. Instead, he said that individuals would automatically be enrolled if they lost their jobs.

But Biden has drawn criticism for other stumbles. And another rival, Sen. Cory Booker of New Jersey, backed Castro after the debate and raised further questions about Biden’s ability to carry the banner for the Democrats into 2020.

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"I think we are at a tough point right now, because there’s a lot of people concerned about Joe Biden’s ability to carry the ball all the way across the end line without fumbling," Booker told CNN in an interview. "And I think that Castro had really legitimate concerns about can he be someone in a long grueling campaign… and has every right to call out."

A clip of that Booker interview appears in the Trump campaign video.

Fox News' Paul Steinhauser contributed to this report.