(CNN) Joe Biden's campaign has offered its first response after President Donald Trump's personal attorney Rudy Giuliani said he would make a now-canceled trip to Ukraine to urge the country to investigate the Democratic presidential candidate.

"It's great to see all these strong progressive voices stand up to this attempt at a blatantly political smear which in and of itself reflects the urgent need for change and to restore the soul of the country," a Biden campaign official told CNN.

Friday, Sen. Elizabeth Warren and former Rep. Beto O'Rourke were among the 2020 Democratic contenders to express concern about Giuliani's efforts.

"I just think it is highly unethical for the President's personal lawyer to go meet with officials from foreign government to see if they can influence somehow the upcoming presidential election," Warren said in Kermit, West Virginia. "We've had enough of that and Rudy Giuliani should just back off."

In New Hampshire, O'Rourke said Giuliani's proposed trip to Ukraine was "so very troubling, very disappointing, and and yet not a total surprise, given this President's behavior and the pattern that he'd already set."

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