The first 2020 presidential debate could be a battle of the brains.

Former Vice President Joe Biden said Thursday that he’s eager to debate President Donald Trump, mocking his intelligence.

“I can hardly wait. I can hardly wait to deal with what he refers to himself as a ‘stable genius,'” Biden told NBC affiliate WBRE at a campaign stop in Pennsylvania. “I can hardly wait to debate him.”

Trump, who has often boasted of his “very, very large brain,” called himself a “very stable genius” in a 2017 tweet in response to media reports about his mental acuity, which in turn became an Internet meme and the title of a book by Washington Post political reporters Philip Rucker and Carol Leonnig.

Trump and his campaign have also pulled no punches going after Biden’s mental acumen.

“Here’s a guy that doesn’t talk. Nobody hears him and whenever he does talk he can’t put two sentences together,” Trump said of Biden at a Fox News town hall last month.

Trump’s reelection campaign has also produced ads aimed at questioning Biden’s mental sharpness. Biden has pushed back at those claims, telling The Columbus Dispatch in March, “My mental acuity is fine.”

Earlier this month, the Biden campaign announced it officially committed the presumptive Democratic candidate to participate in no more than the three previously scheduled presidential debates this fall, the same as in years past. This move preemptively rebutted any likely requests from Trump to have more debates.