President Trump attacked 2020 White House candidate Joe Biden ahead of Wednesday's first Democratic primary debate, assailing the onetime vice president's role in passing the 1994 Violent Crime Control and Law Enforcement Act.

Aboard Air Force One, en route to Osaka, Japan, for the G-20 summit, Trump tweeted criticism of Biden for his past, hard-line stance on criminal justice reform. The president was referencing Biden's key role in passing legislation that critics say has unfairly led to the mass incarceration of minorities.

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"Ever since the passage of the Super Predator Crime Bill, pushed hard by @JoeBiden, together with Bill and Crooked Hillary Clinton, which inflicted great pain on many, but especially the African American Community, Democrats have tried and failed to pass Criminal Justice Reform," Trump said. "They came to me asking for help, and I got Criminal Justice Reform passed, with help from both Republicans and Democrats. Many said that nobody but President Trump could have done this. All previous administrations failed. Please ask why THEY failed to the candidates!"

Biden is set to take the stage alongside nine other candidates on Thursday in Miami for the second of this week's two primary debates. Some critics have called him out of step with an increasingly progressive Democratic Party.

Trump is not alone in his criticisms of Biden.

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New York City Mayor Bill de Blasio and Sen. Kamala Harris, D-Calif., have both blasted their party rival over his input on the bill.

For his part, Biden has continued to defend his stance, even after then-President Bill Clinton admitted he "made the problem worse" in an apology in 2015.