Sen. Lindsey Graham Lindsey Olin GrahamHarris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' Sunday shows preview: Lawmakers prepare for SCOTUS confirmation hearings before election Confirmation hearing for Trump's Supreme Court pick to start Oct. 12 MORE (R-S.C.) on Tuesday said he's "1,000 percent confident" Russia was responsible for hacking the Democratic National Committee (DNC) as part of an effort to interfere in the 2016 election, dismissing the theory that Ukraine played a role in the breach.

The comments from Graham come amid a House impeachment inquiry into President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE's dealings with Ukraine and whether he conditioned military aid on the country opening investigations that benefited him politically.

Trump and some of his GOP supporters in Congress have pushed a conspiracy theory that Ukraine tried to meddle in the 2016 election to help Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonThe Memo: Trump furor stokes fears of unrest Bloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close MORE.

"It was the Russians. I'm 1,000 percent confident that the hack of the DNC was by Russian operatives, no one else," Graham told reporters on Capitol Hill.

"I have no evidence [Ukraine] did. Russia stole the emails, not the Ukraine," he added.

Asked about whether Trump was muddying his defense by pushing the claim, Graham said he thinks it's "always wrong to say things that can't be proven."

The conspiracy theory that Ukraine hacked the DNC has gained increased attention in recent months. Trump referenced the claim during a July 25 phone call with Ukrainian President Volodymyr Zelensky that is now at the heart of House Democrats' impeachment inquiry.

In the call, Trump urged Zelensky to look into CrowdStrike, an internet security company that initially examined the breach of the DNC servers in 2016.

Tom Bossert, a former homeland security adviser in the Trump administration, said in late September that the allegation linked to CrowdStrike was a "completely debunked" conspiracy theory. Fiona Hill, a former top Russia analyst for the White House, also testified last month that the idea that Ukraine interfered in the election is a "fictional narrative that has been perpetrated and propagated by the Russian security services themselves."

Intelligence officials have also reportedly briefed senators that Russia engaged in an effort to frame Kyiv for its election interference.

Trump has, meanwhile, continued to float the allegation, claiming in a Fox News appearance last month that officials gave a DNC server to "CrowdStrike, which is a company owned by a very wealthy Ukrainian." CrowdStrike is a U.S.-based company.

Graham, an outspoken Trump supporter, said that the unfounded allegation likely stems from confusion over media reports about Ukrainian officials' communications with the DNC, though he said that "nobody from the intelligence community has ever told me that that happened."

While the South Carolina senator pushed back against Trump's unsubstantiated claims, Graham has repeatedly voiced support for the president amid the impeachment inquiry.