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’s personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE said he doesn’t think former Vice President and current 2020 frontrunner 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 is capable of being president because he's not "smart enough."

“I don’t think the guy’s smart enough to be president of the United States,” Giuliani told Hill.TV during an interview that aired on Monday. “I’ve known Joe for a long time.”

The former New York City mayor also doubled down on calls for the Biden family to be investigated. He cited some business dealings by Biden's son, Hunter Biden, that took place in China and Ukraine when his father was still vice president.

“I also think his activities in Ukraine and China should be seriously investigated,” Giuliani told Hill.TV. “It’s a Democratic press that’s protecting him and they’re actually going easy on him.”

The Biden campaign declined Hill.TV’s request for comment.

Trump allies and conservatives have long claimed that the Biden's have been involved corrupt business dealings. Earlier this year, conservative author Peter Schweizer claimed that Hunter Biden inked a deal with the Chinese government in 2013, just days after then-Vice president Joe Biden visited the country.

Their concerns also center around whether Joe Biden demanded the resignation of former Prosecutor General Viktor Shokin when Shokin was investigating Burisma, where Hunter Biden was a board member at the time. But Ukraine’s top prosecutor said in May that he found no evidence of wrongdoing.

Both Biden and his son have also shot down the accusations. In an interview with ABC News earlier this month, Hunter Biden directly addressed some of allegations, calling them “demonstrably false," and said they were narratives that have been created by "the right-wing political apparatus."

However, Giuliani said that he hasn’t ruled out a trip to Ukraine to meet with the country’s leaders and ask them to pursue an investigation.

In May, Giuliani announced and then subsequently cancelled plans to travel to Ukraine to ask the Ukrainian government to look into the origins of special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s Russia probe and Biden’s past influence in the country.

“I could — I like the Ukraine,” he told Hill.TV. “I think the Ukraine is a great country, I think it is riddled with corruption.”

Giuliani’s comments come amid reports that he helped establish a backchannel with top Ukrainian officials.

Buzzfeed News reported Monday that two U.S. operatives reporting to Giuliani met with Ukrainian officials in an attempt to gather information to use in the 2020 presidential election. They also reportedly sought to push Ukrainian prosecutors to investigate Biden.

Story updated at 5:00 P.M. EST.

—Tess Bonn