"But Nixon had a pipeline to Saigon, where the South Vietnamese president, Nguyen Van Thieu, feared that Johnson would sell him out. If Thieu would stall the talks, Nixon could portray Johnson's actions as a cheap political trick. The conduit was Anna Chennault, a Republican doyenne and Nixon fund-raiser, and a member of the pro-nationalist China lobby, with connections across Asia.
"'! Keep Anna Chennault working on' South Vietnam, Haldeman scrawled, recording Nixon's orders. 'Any other way to monkey wrench it? Anything RN can do.'"
John A. Farrell in The New York Times discusses notes written by H. R. Haldeman about Vietnam in 1968 that establish that Richard "Nixon directed his campaign's efforts to scuttle the peace talks."
And Colin Schultz in a 2013 Smithsonian article cites other evidence.