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 lawyer Rudy Giuliani said late Wednesday that special counsel Robert Mueller's investigation could be over by September and predicted it is "going to blow up on them."

"The real story is not that this case isn’t going to fizzle," he told Fox News host Sean Hannity during a discussion of why Mueller's terms for an interview with Trump were rejected. "It's going to blow up on them. The real question is, what we talked about before, there's a lot more to what they did that nobody knows about yet."

Giuliani added there is "a lot more to the obstruction of justice, to the collusion, to the fake dossier," referring to the controversial dossier compiled by former British intelligence agent Christopher Steele.

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Giuliani often falsely claims that Mueller's probe started with the dossier, which contains unverified allegations about Trump's ties to Russia.

"Can it get any worse?" Giuliani said. "I mean, what ... we need to know [is] that this is a totally illegitimate investigation based on a report, a dossier that was paid for by 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 and the Democrats — probably the biggest illegality so far, the biggest collusion so far."

"Completely made up," he added. "Led to nothing except several fraudulent FISA [Foreign Intelligence Surveillance Act] wires."

Deputy Attorney General Rod Rosenstein Rod RosensteinDOJ kept investigators from completing probe of Trump ties to Russia: report Five takeaways from final Senate Intel Russia report FBI officials hid copies of Russia probe documents fearing Trump interference: book MORE appointed Mueller as special counsel to investigate possible ties between the Trump campaign and Russia after Trump fired former FBI Director James Comey James Brien ComeySteele Dossier sub-source was subject of FBI counterintelligence probe Judge will not dismiss McCabe's case against DOJ Democrats fear Russia interference could spoil bid to retake Senate MORE in 2017.

Giuliani on Fox called the Mueller probe "a different kind of Watergate."

"I believe that when this plays out over the next year or two, it's not going to be about President Trump," Giuliani said. "It’s going to be about all the things they did."

"My sources are telling me that when the American people get to the bottom of all of this, it will shock the heart, the soul, and the mind of any fair-minded American," Hannity replied.

Giuliani has said in recent days that Trump's legal team is nearing the end of negotiations over an interview between Mueller and the president.