One other incident, right at the end of the campaign, shows some of the differences between 1968 and 2008.
One of Nixon's fundraisers was an Asian lady who took her role as "insider" a little too seriously. Apparently believing that she was somehow empowered to speak for the campaign, she set about sabotaging the Paris peace talks by claiming Nixon wasn't going to be bound by the outcome.
There is no evidence that Nixon was anything other than horrified to find this out, and not just for the political implications. Both parties - with the exception of Eugene McCarthy, who didn't really want the job - tended to avoid outright criticism of the war or the President, and to avoid anything that could interfere with the conduct of foreign policy up to the election.
Humphrey found out about this mischievous Nixon fundraiser - and sat on the information. He believed that Nixon couldn't have countenanced this behavior, and that it would be unfair to use it against him. Meanwhile, the Nixon camp knew it had no plausible or persuasive response should Humphrey choose to go public.
Compare that Al Gore's behavior in 2000, panting to get news of an ancient DUI, leaked to him by a partisan judge in Maine, to the press before the weekend news cycle.
Humphrey had labored in Johnson's shadow, unwilling to publicly criticize the war or the negotiations until October of 1968. To the extent that there's a parallel in 2008, John McCain has at least avoided that trap, supporting the effort while making clear his differences with the administration on its conduct in Iraq.