Wikipedia (en)
Members of the 2016 Trump campaign had several meetings with individuals who were perceived to have Russian connections.
On June 9, 2016, a meeting was held in Trump Tower in New York City between three senior members of the Donald Trump presidential campaign – Donald Trump Jr., Jared Kushner, and Paul Manafort – and at least five other people, including Russian lawyer Natalia Veselnitskaya. The meeting was arranged by publicist and long-time Trump acquantiance, Rob Goldstone on behalf of his client, singer-songwriter Emin Agalarov. It was disclosed to U.S. government officials when Kushner filed a revised version of his security clearance form.
Donald Trump Jr. initially told the press that the meeting was held to discuss adoptions of Russian children by Americans. On July 8, 2017, Trump Jr. tweeted that he agreed to the meeting with the understanding that he would receive information damaging to Hillary Clinton, and that he was conducting opposition research. Goldstone had stated in his email that the Russian government was involved. Robert Mueller, the special counsel of the Department of Justice in charge of Russia-related investigations, is investigating the emails and the meeting, and their relation to the Russian interference in the 2016 United States elections.
Prior to that meeting, Trump campaign advisor George Papadopoulos met at least twice with a professor who said he had access to "dirt" on Hillary Clinton in the form of "thousands of emails." This occurred before the hacking of the DNC computers had become public knowledge. Papadopoulos later shared this information with at least two other people, including an Australian diplomat to Great Britain. At a meeting on March 24, 2016, the professor brought along a Russian woman, Olga Polonskaya. Papadopoulos made multiple unsuccessful attempts to set up meetings in Russia between Trump or members of his campaign and Russian officials. He communicated his proposals and interactions to several Trump campaign officials. In October 2017 he pleaded guilty to one count of making false statements to the FBI about his actions.