Two top Republican senators have asked the Justice Department to investigate allegations that Democrats sought dirt on Donald Trump from Ukrainian officials during the 2016 election. In a letter to Attorney General William Barr released Monday, Sens. Ron Johnson of Wisconsin and Chuck Grassley of Iowa push the Justice Department to open a probe, saying they have “concerns about foreign assistance in the 2016 election that have not been thoroughly addressed.”

“Ukrainian efforts, abetted by a U.S. political party, to interfere in the 2016 election should not be ignored. Such allegations of corruption deserve due scrutiny, and the American people have a right to know when foreign forces attempt to undermine our democratic processes,” the senators wrote in the letter.

“The Justice Department has yet to inform Congress and the public whether it has begun an investigation into links and coordination between the Ukrainian government and individuals associated with the campaign of Hillary Clinton or the Democratic National Committee. Ukrainian efforts, abetted by a U.S. political party, to interfere in the 2016 election should not be ignored,” the two senators wrote in the letter, dated September 27. “Are you investigating links and coordination between the Ukrainian government and individuals associated with the campaign of Hillary Clinton or the Democratic National Committee? If not, why not?”

The senators claim Alexandra Chalupa, a Democratic consultant, worked with Ukrainian officials to find dirt on Trump in 2016.

“At the center of this plan was Alexandra Chalupa, described by reports as a Ukrainian-American operative ‘who was consulting for the Democratic National Committee’ and who reportedly met with Ukrainian officials during the presidential election for the express purpose of exposing alleged ties between then-candidate Donald Trump, Paul Manafort, and Russia.[4] Politico also reported on a Financial Times story that quoted a Ukrainian legislator, Serhiy Leschenko, as saying that Trump’s candidacy caused ‘Kiev’s wider political leadership to do something they would never have attempted before: intervene, however indirectly, in a U.S. election,'” the letter says.

Chalupa denies the allegations. “During the 2016 US election, I was a part-time consultant for the DNC running an ethnic engagement program,” she told CNN in July. “I was not an opposition researcher for the DNC, and the DNC never asked me to go to the Ukrainian Embassy to collect information.”

But the senators cited a news article from The Hill claiming otherwise.

“In addition, in May 2016, Chalupa emailed a DNC official stating that she met with 68 Ukrainian investigative journalists about Manafort and that there would be ‘[a] lot more coming down the pipe,'” the senators wrote. “Less than a month later, the ‘black ledger’ identifying payments made to Manafort from Ukrainian politicians was announced in Ukraine.[11] And finally, Nellie Ohr, the wife of Justice Department official Bruce Ohr, stated during a congressional interview that Fusion GPS used Serhiy Leschenko, a Ukrainian politician that admitted Ukraine intervened in the 2016 election, as a source for derogatory material against then-candidate Trump.”

The senators asked for a response by Oct. 14.

Read the full letter below: