FIRST ON FOX Senate Republicans plan to launch their own investigation next month that delves into the alleged "conspiracy" behind former President Joe Bidens cognitive decline.Senators Eric Schmitt, R-Mo., and John Cornyn, R-Texas, announced plans to hold a Senate Judiciary hearing June 18 to look into the alleged cover-up of the 82-year-old former presidents mental decline while in office by the media and those closest to him.The lawmakers are still gathering witnesses for the probe, which would be the first full congressional committee hearing on the subject."Its time to expose how a cadre of Biden aides and family members were the de facto commander in chief, while President Biden was sidelined," Schmitt said in a statement to Fox News Digital. "I look forward to getting the American people the answers they deserve."SCOOP: GOP PUSH FOR NEW HOUSE COMMITTEE TO PROBE BIDEN DECLINE 'COVER-UP' GAINS STEAMBoth lawmakers contend Bidens decline was hidden for "years."Cornyn argued the country depended "on having a president who has the mental capacity to do the job, and it's clear that President Biden did not, so we must use this hearing to uncover the facts."KEY BIDEN STAFFERS ASKED TO TESTIFY ON ALLEGED ROLE IN MENTAL DECLINE COVER-UP"For this conspiracy between the mainstream media, Joe Bidens family and his inner circle to have hidden the impairment of the president of the United States for years, and lied consistently to the American people about his capacity to make decisions, which are solely vested by the Constitution, is unacceptable," Cornyn said in a statement to Fox News Digital.Schmitt and Cornyn join a growing chorus of Republicans demanding answers about what really went on behind the scenes during Bidens presidency.In the House, lawmakers are pushing to create a select committee that would investigate the Biden administrations alleged cover-up.Rep. Buddy Carter, R-Ga., is leading the charge to create the panel and introduced legislation Thursday to start the committee that would dive into "the potential concealment of information from the American public" regarding Bidens health.And House Oversight Committee Chair James Comer, R-Ky., has called on several high-ranking staffers from the Biden White House to participate in transcribed interviews regarding their alleged roles in covering up the former presidents decline.Comer called on Neera Tanden, the former director of the Domestic Policy Council; former assistant to the President and deputy chief of staff Annie Tomasini; former senior adviser to the first lady Anthony Bernal; former deputy director of Oval Office operations Ashley Williams; and Bidens physician, Dr. Kevin OConnor, to participate.The growing fervor among Republicans to uncover whether Bidens allies and family hid concerns about his health from the public comes after the release of "Original Sin" by CNN host Jake Tapper and Axios reporter Alex Thompson.Their book claimed the Biden White House was trying to control the narrative about the former presidents health and that his allies worked to cover up his decline.