Republicans have scrambled in recent weeks to come up with responses to revelations that the Trump administration withheld a $250 million security assistance package to Ukraine as the President and Giuliani pushed the country's leadership to manufacture political dirt.
Text messages between top USA diplomats that were released by the House Intelligence Committee have corroborated the whistleblower's claim that Giuliani was involved in Trump's push to have Ukrainian President Volodymyr Zelensky investigate the Bidens.
"It is time for the Senate to inquire about corruption and other improprieties involving Ukraine", Senator Lindsey Graham said in a series of tweets, mentioning specifically the firing of Ukraine's former prosecutor Viktor Shokin.
Graham's decision came just hours after the State Department blocked U.S. Ambassador to the European Union Gordon Sondland from appearing before the House panels leading the investigation.
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The committee is led by Lindsey Graham.
Graham's counter-attack on the House's impeachment inquiry came after days of pressure from top Trump allies including Donald Trump Jr. for Graham to act. The top Democrat on the Senate Judiciary Committee, Sen. Kamala Harris (D-Calif.), Cory Booker (D-N.J.) and Amy Klobuchar (D-Minn.) - an opportunity to question him.
"We'll hear from Giuliani and then determine what, if any additional witnesses need to be called", said Graham spokeswoman Taylor Reidy.
"Good. I have questions", Harris tweeted. The Democratic chairmen of the committees said they would subpoena Sondland for his testimony as well as communications from his personal devices that have been turned over to the State Department.
Republicans have sought to pivot the scandal's focus away from Trump's efforts to get other nations' help in the presidential election and are instead focusing on the alleged wrongdoing by Biden and his son of using their influence for personal gain. Graham has moved to seize the opportunity and start investigating what the Judiciary Chairman has called "disturbing allegations" and "corruption" surrounding the firing of the Ukrainian prosecutor investigating Hunter Biden.