Democratic presidential candidate Beto O'Rourke said Thursday that the primary frontrunner, Joe Biden, represented a return to the past and that the country can "do much better."

The comments, made during a morning TV interview, were O'Rourke's most direct and thorough criticism yet of Biden — or any rival, for that matter. The exchange on MSNBC's "Morning Joe" began when host Willie Geist asked O'Rourke about his differences with Biden, the former vice president — and the former El Paso congressman launched into a rebuttal of the notion that Biden is the party's best hope to defeat President Donald Trump.

"You cannot go back to the end of the Obama administration and think that's good enough," O'Rourke said, adding that the country "had real problems before Donald Trump" was elected president. "We cannot return to the past. We cannot simply be about defeating Donald Trump."

Asked if Biden is a return to the past, O'Rourke responded without hesitation: "He is. And that cannot be who we are going forward. We've got to be bigger, we've got to be bolder, we've got to set a much higher mark and be relentless in pursuing that."

O'Rourke's poll numbers have slid since Biden entered the race, and O'Rourke's criticism of Biden tests his insistence on running a positive campaign and not defining himself in contrast to anyone else, particularly fellow Democrats. In the early days of his candidacy, O'Rourke declined to criticize Biden and even encouraged him to enter the race, saying the country would "be very lucky" to have Biden run.

O'Rourke struck a much different tone in the "Morning Joe" interview. After agreeing Biden represented a return to the past, O'Rourke was asked if Biden, a former U.S. senator, should apologize for his 2002 vote in favor of the Iraq War — and O'Rourke continued to hammer Biden.

“Look, you’ve got to ask yourself where Joe Biden is on the issues most important to you," O'Rourke said. "Did he support the war in Iraq that forever destabilized the Middle East? Does he really believe that women of lower income should be able to make their own decisions about their own body, be able to afford health care to do that? He supported the Hyde Amendment" — which bans federal funding for abortions — "he now opposes the Hyde Amendment. On China, he sees China as no threat, nothing to worry about, and now seems to be changing his message on that."

"So I’m not exactly sure what he believes or what he should apologize for," O'Rourke added. "I only know that this country should be able to do far better."

O'Rourke was among the 2020 candidates who criticized Biden for standing by his support of the Hyde Amendment last week, calling the former vice president "absolutely wrong on this one." Biden quickly reversed himself and came out against the law.

Both Biden and O'Rourke could come face to face soon, with the first primary debates set to take place over two nights, June 26-27, in Miami.

Biden's campaign did not immediately respond to a request for comment on O'Rourke's MSNBC interview.