Senate Homeland Security and Governmental Affairs Committee Chairman Ron Johnson (R-Wis.) opened the door on Thursday to subpoenaing a cadre of top Republican targets as part of his panel's oversight work.

Pressed if he would issue subpoenas for House Intelligence Committee Chairman Adam Schiff (D-Calif.), former Vice President Biden or his son Hunter Biden or the whistleblower at the center of the impeachment inquiry, Johnson stressed that he was still trying to collect information.

"I don't really want to make news on your program because I'm working with Senator Grassley's staff, but we're having meetings in terms of what our next steps are," Johnson told WSAU, a Wisconsin radio station on Thursday.

"I'm not going to get out ahead of my skis here. ...In order to bring in witnesses for questioning you want to lay the groundwork," Johnson continued. "[A] subpoena is the last step in the process, you go through a multiple step process."

Asked by the talk radio host if he was willing to say that the Bidens, the whistleblower and Schiff would be subpoenaed "once he got to the bottom of all this," Johnson added "unless they cooperate willingly, and that may happen."

"If not, yeah I have that subpoena power and I'm not afraid to use it," he said.

Asked if he was willing to say he would use it, Johnson added: "I will use it."

Johnson and Senate Finance Committee Chairman Chuck Grassley (R-Iowa) have fired off a flurry of oversight letters, including requesting any State Department records involving Hunter Biden or Ukraine gas company Burisma.

Johnson's radio interview comes as conservatives have fumed over the House's impeachment inquiry, which is investigating whether not Trump tied Ukraine aid to the country opening an investigation into former Vice President Biden and his son Hunter Biden.

House Republicans tried to call the whistleblower, who filed a complaint that helped guide the investigation, as well as Hunter Biden as witnesses in the public impeachment inquiry hearings. But Democrats rejected their request.

Senate Judiciary Committee Chairman Lindsey Graham (R-S.C.) has also come under fierce pressure from the right to call Schiff to testify before his panel. Graham has ruled out calling Schiff, but said during a Fox News interview this week that he believes the Democratic lawmaker should be called as part of an impeachment trial.

Sen. Rand Paul (R-Ky.) separately told reporters on Thursday that he was considering forcing a vote on the Senate floor to try to allow the White House to call its preferred witnesses, including Hunter Biden.

"I believe very strongly the president should be able to call his own witnesses. ...The rules that are put forward will be amendable, and so yes I will consider strongly that the president should get his full due process, which to me means bringing in his own witnesses," Paul said.