Washington (CNN) Former Texas Rep. Beto O'Rourke on Thursday knocked his highest polling competitor for the Democratic presidential nomination, former Vice President Joe Biden, saying the frontrunner would be a return to the past.

"You cannot go back to the end of the Obama administration and think that that's good enough," O'Rourke said on MSNBC's "Morning Joe." "As much of a horror show as Trump has been -- his racism, the disaster of his foreign policy, his punishment of farmers and workers here in this country -- we had real problems before Donald Trump became President."

O'Rourke's criticism of Biden was emphatic.

"We cannot return to the past," O'Rourke said. "We cannot simply be about defeating Donald Trump."

O'Rourke took Biden to task on deportation and racial wealth inequality under the Obama administration -- amounting to an outright argument against Biden's candidacy from O'Rourke, who has sought to recharge his own campaign ahead of the debates this summer.

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