President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE on Wednesday touted the passage of criminal justice reform under his administration roughly an hour before the start of the first Democratic presidential primary debate, calling for candidates to be asked why past administrations failed to do the same.

In a pair of tweets sent aboard Air Force One, Trump specifically knocked his 2016 opponent, Hillary Clinton Hillary Diane Rodham ClintonFox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio Trump, Biden court Black business owners in final election sprint The power of incumbency: How Trump is using the Oval Office to win reelection MORE, as well as 2020 candidate and former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE, who will not be onstage until Thursday night.

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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 tweeted, noting that a bipartisan criminal justice reform bill was passed during his presidency.

"Many said that nobody but President Trump could have done this," he added. "All previous administrations failed. Please ask why THEY failed to the candidates!"

....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! — Donald J. Trump (@realDonaldTrump) June 26, 2019

Trump made the comments while en route to Japan for the Group of 20 summit. He had tweeted minutes earlier that his campaign team would be offering live reaction as the debate unfolded because he was "off to save the Free World."

The president told Fox Business Network on Wednesday morning that he would watch the debate "because I have to," despite it being a "very unexciting group of people."

The first night of the debates will include Sen. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Mass.), former Rep. Beto O'Rourke Beto O'RourkeJimmy Carter says his son smoked pot with Willie Nelson on White House roof O'Rourke endorses Kennedy for Senate: 'A champion for the values we're most proud of' 2020 Democrats do convention Zoom call MORE (D-Texas), Sen. Cory Booker Cory Anthony Booker3 reasons why Biden is misreading the politics of court packing Bipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility MORE (D-N.J.) and New York City Mayor Bill de Blasio Bill de BlasioOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right EPA threatens to close New York City office after Trump threats to 'anarchist' cities New Year's Eve in Times Square to be largely virtual amid pandemic MORE (D).

Thursday's debate will see Biden go head-to-head with Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.), Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.) and South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE (D).

The president has previously targeted Biden over his support of the 1994 crime bill, and has fixated on the former vice president as the likely front-runner.

Several Democratic candidates, including Warren, Booker and O'Rourke, have offered plans detailing prison reform or further changes to the criminal justice system.