Not exactly true.
It did happen, just not with or about Trump.
The investigation was done by Obama to use against Hillary in the battle to see who would be the Democrat Party Choice for President back for the 2012 election. She backed down, he won the nomination. The report was shelved.
When Trump won, the report was rewritten using Trump's name instead of Hillary's. The report was sent to Britain to 'launder' it's source. McCain presented it as if it were original and done by the British Intelligence Services.
2012? clinton tried to unseat obama?