Trump has previously criticized US Attorney General Jeff Sessions for failing to push forth an investigation into alleged Ukrainian meddling in the 2016 US presidential election.
According to previous media reports, the DNC hired Chalupa to look into links between Manafort and the administration of former Ukrainian President Victor Yanukovych.
Chalupa left the DNC in 2016, but reportedly continued to provide the DNC and then-Democratic candidate Hillary Clinton's campaign with information about Manafort.
US federal law and Federal Election Commission regulations prohibit any person from knowingly soliciting, accepting or receiving money or help from a foreign national.
The Ukrainian embassy in Washington, DC has denied that the government of Ukraine helped any candidate in the election.
President Trump has been dogged by accusations that Russia interfered in the election and colluded with Trump's campaign team to influence the outcome of the vote.
Russia has repeatedly denied meddling in the election and insists that it does not interfere in the internal affairs of other countries.
Trump has also strongly rejected charges that his campaign team colluded with Moscow during the run-up to the vote.
