Graham warns Giuliani: 'I hope you know what you're talking about'

Sen. Lindsey GrahamLindsey Olin GrahamSenate GOP mulls speeding up Trump impeachment trial Democratic group plans mobile billboard targeting Collins on impeachment Paul predicts no Republicans will vote to convict Trump MORE (R-S.C.) warned on Wednesday that if Rudy GiulianiRudy GiulianiDems plan marathon prep for Senate trial, wary of Trump trying to 'game' the process House Democrats release second batch of Parnas materials Republicans will pay on Election Day for politicizing Trump's impeachment MORE, President TrumpDonald John TrumpNational Archives says it altered Trump signs, other messages in Women's March photo Dems plan marathon prep for Senate trial, wary of Trump trying to 'game' the process Democratic lawmaker dismisses GOP lawsuit threat: 'Take your letter and shove it' MORE's personal lawyer, is going to publicly suggest a "cover-up" involving the Bidens and Ukraine "then I hope you know what you're talking about.”

Graham’s comments come after Giuliani took a trip to Ukraine this month and met with a host of former and current officials as part of an effort to unearth more dirt on Trump's political rivals, including 2020 presidential candidate Joe BidenJoe BidenSanders to headline Iowa event amid impeachment trial Hillicon Valley: Biden calls for revoking tech legal shield | DHS chief 'fully expects' Russia to try to interfere in 2020 | Smaller companies testify against Big Tech 'monopoly power' Hill.TV's Krystal Ball on Sanders-Warren feud: 'Don't play to the pundits, play to voters' MORE.

Trump’s efforts to get Kyiv to announce investigations into the Biden family and unfounded accusations that Ukraine interfered in the 2016 elections are at the center of Democrats’ impeachment efforts against him.

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"I don't know what Rudy's got, but I'm going to send him a letter. If you're going to go on national television and tell the country that you've found evidence of a cover-up, then I hope you know what you're talking about,” Graham told reporters.

"I like Rudy a lot, but we're going to have to watch what we say,” he added.

Graham has invited Giuliani to testify before the Senate Judiciary Committee over his concerns about corruption in Ukraine. He reiterated on Wednesday that Trump’s lawyer has an “open invitation” before the panel he chairs. 

"If he comes, you gotta be willing to ask questions about your conduct. It's just not good for the country to make these accusations on cable television without them being tested,” Graham added. 

Giuliani told The Washington Post that Trump has asked him to brief GOP senators and the Justice Department on his findings in Ukraine. A source told The Wall Street Journal that Giuliani told the president that his recent trip produced "more than you can imagine."  

Trump and his allies have latched onto Hunter Biden's connection to Ukraine, where he served on the board of an energy company, as the former vice president seeks the Democratic nomination to challenge Trump in 2020. There's no indication Joe Biden was acting with his son's interests in mind when he called for the ouster of a Ukrainian prosecutor accused of corruption, and the former vice president has denied any such motivations.