I'm sure the crowd was 90% Democrats and 10% NeverTrump Republicans. Of course the Democrats are devastated to lose their champion anti-Trump crusader. McCain was certainly not a Republican. But while he was much more Democrat than anything else, he was not a die-hard Democrat. He was an equal opportunity backstabber.
McCain was in it for McCain. Nothing more and nothing less than that. Whatever he felt benefited his petty vendettas or pumped his ego, that is what he was for. Regardless of which political side it fell on.