As Philip Bobbitt shows in his supplement to Charles Black’s landmark study of impeachment, a “conspiracy to pervert the course of a presidential election” by “acting in league with a hostile foreign power” is clearly a basis for removal. So, too, is any false statement made to impede an investigation into this kind of conspiracy—including false statements to the public. A clear precedent is the article of impeachment on obstruction passed by the House Judiciary Committee in the proceedings against Richard Nixon. It included a charge that Nixon had made “false and misleading public statements,” which were “contrary to his trust as president and subversive of constitutional government.”
It is entirely possible that Trump has made “false and misleading public statements” of exactly that sort.
The president has repeatedly denied not only any legal offense of “collusion” with Russia leading up to the 2016 election—however he may understand the term—but also any contact at all between his campaign and the Kremlin. In November 2016, Hope Hicks spoke for him and his campaign in saying that there was “no communication between the campaign and any foreign entity during the campaign.”