By now, likely you have heard about this.
Scenario: South Vietnam President Thieu is being pressured towards the Paris peace talks, under the cloud that the likeliest result is unfavorable to his regime. Candidate Nixon, with the connivance of Kissinger, sends a back channel message via Claire Chennault to Thieu (toot!).
Substance of message: hold out, stiff the talks, and when we win we will commit to enough military force to make sure that the North Vietnamese cut you a better deal.
And so the war went on.
There is considerable evidence to suggest that this scenario is essentially correct. Cites available.
Does this, or does it not, constitute treason, as you define it?