Trump's son confirmed the truth of the story by releasing copies of his own emails on his personal Twitter account. Those emails had originally been copied to Trump's campaign manager and son-in-law to set up a meeting with the Kremlin emissary, which all parties eventually attended.
This is a huge revelation. Lawyers interviewed by Politico (link here) said that Trump's son, his son-in-law, and his campaign manager could be prosecuted for violating federal criminal statutes prohibiting a campaign from "the solicitation or acceptance of anything of value from a foreign national, as well as a conspiracy to defraud the United States."
So that brings us to the ten lies. NBC helpfully compiled a list (link here) of ten times in the last two months alone that the President has lied about collusion with Russia.
Trump doubled down on these lies, then again, and again, and again and again, as did all of his staff repeatedly. His own family was colluding but Trump just kept on lying.