The Senate Intelligence Committee plans to call the whistleblower whose complaint was the impetus for impeachment proceedings against President Trump, according to a top Republican senator.

With impeachment headed to a likely acquittal next week, Sen. Lindsey Graham described on Sunday how Republicans in the chamber are gearing up for investigations on three fronts.

"The Senate Intel Committee under Richard Burr has told us that we will call the whistleblower," the South Carolina Republican said on Fox News's Sunday Morning Futures.

"I want to find out how all this crap started," he added.

The impeachment effort began to take root with the emergence last year of a whistleblower complaint raising concerns about a July phone call between Trump and Ukrainian President Volodymyr Zelensky in which the American leader pressed his Ukrainian counterpart to investigate the Bidens and other Democrats. The complaint, which the intelligence community inspector general determined to be urgent and credible, was submitted by a CIA analyst whose identity has never been publicly confirmed.

Republicans have accused House Intelligence Committee Chairman Adam Schiff, who is now the lead impeachment manager, of being "complicit" with the whistleblower because the person met with a House Intelligence Committee aide seeking guidance before filing the complaint and because the California Democrat recruited two former National Security Council aides who worked alongside the CIA official some believe to be the whistleblower at the NSC in the Obama and Trump administrations.

"If the whistleblower is a former employee — associate of Joe Biden, I think that would be important. If the whistleblower was working with people on Schiff’s staff that wanted to take Trump down a year-and-a-half ago, I think that would be important. If the Schiff staff people helped write the complaint, that would be important. We’re going to get to the bottom of all of this to make sure this never happens again," Graham said.

[Read more: 'Bro-like': Schiff aide was White House friend of alleged whistleblower Eric Ciaramella]

Sen. Richard Burr, who hails from North Carolina, said last year he "absolutely" wanted to hear from the whistleblower, but Republican members of his panel were split on the matter as House impeachment proceedings were underway. When asked for comment, a representative for Burr pointed the Washington Examiner to past statements by the chairman, including him saying the whistleblower had not yet agreed to appear before the Senate Intelligence Committee and stressing that the panel does everything it can to "protect" whistleblowers and witnesses.

Impeachment proceedings began last fall with Democrats accusing Trump of improperly leveraging a White House meeting and nearly $400 million in security aid to pressure Ukraine into helping to investigate his political rivals, including former Vice President Joe Biden, who is running for president this year. As Republican allies of the president called for the whistleblower to come forward, Democrats argued that witness testimony and documents moved the impeachment case beyond the whistleblower. Lawyers for the whistleblower warned that identifying their client would put that person's life in danger.

The House charged Trump with abuse of power and obstruction of Congress, but the president's legal team argued that the Democrats' case fell far short of proving impeachable offenses. Trump is now headed toward a likely acquittal on Wednesday after the Senate voted to reject a motion for additional witnesses and documents.

Graham, who is the chairman of the Senate Judiciary Committee and does not reside on the chamber's Intelligence Committee, also described two other investigations that will be taken up by GOP-led panels in the Senate. He said the Foreign Relations Committee, of which he is also a member, will look into Biden's alleged conflicts of interest, and the judiciary panel will "deal with all things FISA."

"Let me tell Republicans out there: You should expect us to do this. If we don’t do it, we’re letting you down. I guarantee you — if the shoe were on the other foot, Democrats would be eating us alive if Republicans had done any of these things," he said.