I believe it was at Cold Harbor where there were horrific casualties suffered including a disastrous third assault where his troops were slaughtered. Grant was quoted as saying," It's been a helluva day. We'll get 'em tomorrow". No one accused him of sticking with a disastrous policy. War is awful.
Grant's 'policy' (which was approved by Lincoln) was to wear the Army of Northern Virginia down and force it to fight openly where the superior force of the Army of the Potomac would win. That was not a disastrous policy. The problem was that Lee was too successful getting his army always behind virtually insurmountable entrenchments, and the staff of the Army of the Potomac, from Mead's level on down, was woefully slow in getting things done, and even incompetent - which greatly contributed to Lee's success. Bruce Catton hits this nail on the head in his 'A Stillness At Appomattox'
It wasn't the policy, per se, that caused the war to drag on another year from the date Grant crossed the Rapidan.