Sen. Rand Paul said he will force the Senate to vote on whether they want to hear impeachment testimony from Hunter Biden if his colleagues support hearing from witnesses proposed by Democrats.

Biden, 49, was at the center of President Trump’s request for Ukrainian leaders to investigate his father, Joe Biden, for possible corruption. While the elder Biden was leading diplomatic efforts in Ukraine as Obama’s vice president, the younger Biden received a high-paying position on the board of Burisma, an allegedly corrupt natural gas firm in Ukraine.

Many have questioned how Hunter Biden, who had a documented history of drug abuse and no substantial experience in the energy sector, was qualified for a job on Burisma’s board. Some Republicans have argued that Trump’s request for Ukraine to investigate the Bidens and Burisma was justified.

Paul, 57, argued that Hunter Biden must testify to help Republicans consider whether Trump’s request for an investigation was substantiated by any corruption. Senate Majority Leader Mitch McConnell planned to not call any witnesses forward, but there has been an effort among Republicans, such as Susan Collins, to bring in witnesses such as John Bolton for testimony.

On Monday night, Paul argued that Biden should be included in a list of witnesses, tweeting, “My colleagues can’t have it both ways. Calling for some, while blocking others. If we are going to give a platform to witnesses the Dems demand, I look forward to forcing votes to call Hunter Biden and many more!”

My colleagues can’t have it both ways. Calling for some, while blocking others. If we are going to give a platform to witnesses the Dems demand, I look forward to forcing votes to call Hunter Biden and many more! https://t.co/hrOzVyiG9x — Senator Rand Paul (@RandPaul) January 14, 2020

The Kentucky Republican included a link to a Politico report referencing a private conversation among Senate Republicans during which Paul issued a similar warning.

It remains unclear if GOP senators will call forward any witnesses or if they will stick to McConnell’s plan of moving forward with an expedited impeachment trial. House Speaker Nancy Pelosi is expected to turn over the impeachment this week after withholding the articles since mid-December.

Many House Republicans argued that Hunter Biden should testify prior to the impeachment vote, including Florida Rep. Matt Gaetz, who said, “I don’t want to make light of anybody’s substance abuse issues. I know the president's working real hard to solve those throughout the country. But it's a little hard to believe that Burisma hired Hunter Biden to resolve their international disputes when he could not resolve his own dispute with Hertz rental car over leaving cocaine and a crack pipe in the car.”