You're mistaken
The Senate Cambodia speech at issue occurred when Kerry was a US Senator in the 80s while Reagan was president. It's not the 70s speech when he went around dressed revolutionary chic like Che Guevara.
Senator Kerry attempted to shape US policy away from the Reagan administration and towards his hero communist Daniel Ortega by citing his experience in a covert mission to Cambodia over Christmas. An experience he said was "seared" into his memory, the liar. This was no casual mis-speak.