On July 11–12, 2016, during the Republican National Convention in Cleveland, Ohio, the Trump campaign pushed the Republican Party to change its official policy on Ukraine: no longer proposing sending “lethal weapons” to the Ukrainian army to fend off Russian aggression, but instead, softened to say only “provide appropriate assistance.” Source1 Source2 Trump campaign aide JD Gordon has stated that he advocated for Republican platform changes to soften action against Russia in response to their Ukraine intervention. Gordon said he did so believing it to match Trump’s views, having consulted about the matter with others in the Trump campaign before the convention. Source
On July 18–19, 2016, several Trump campaign members met Russian ambassador Sergey Kislyak at a Global Partners in Diplomacy event, linked to the ongoing RNC. Carter Page testified that he, Jeff Sessions, J.D. Gordon, and George Papadopoulos had a meeting with Kislyak, discussing policy issues. Source Gordon said that their discussion involved Trump’s desire to “reset” the US-Russia relationship, and potential future cooperation regarding ISIS and issues in Syria. Source
Carter Page would later falsely claim that he had “no meetings” with Russian officials in 2016. Source Similarly, during his confirmation hearing for his appointment to Attorney General, Jeff Sessions would testify that during the campaign he did not have any communications with any Russians. Source
Note that Kislyak was under US surveillance, as confirmed by the leaked info about his conversation with Michael Flynn regarding Obama’s new sanctions against Russia. If this surveillance included bugging his mobile phone, it is possible that all his conversations at the RNC are on the record for US investigators. This is speculation, but James Comey stated that the FBI began its investigation into Trump-Russia collusion on July 25, only a week after the RNC. Source If US parties had improper discussions with Kislyak at the RNC this could have been the trigger to launch the investigation.