My opinion is borne out, BTW, by the actual historical facts. The North did not crumble when casualties started to mount. The North in fact did gain the upper hand precisely when the war became a war of attrition following Grant’s assumption of command of the Union Army.
Of course Lee and every confederate general dream would have been a quick victory to end it but realistically he saw that if the high casualties and a prolonged war could make it political then they had a chance at a truce. You’re looking at it in hindsight that the Union didn’t falter and the war of attrition (wearing out the politicians) embolden many in the North and it did but the Anaconda plan and the determination of the North despite the horrific casualties made the attempt of wearing out the “politicans” futile. That’s a fact