I see many posts here lauding McCains bravery and shake my head. This is pretty much a textbook case of slacktivism; a tepid online statement of support with no follow-up actions.
Yes, he disagreed with Trumps actions. This only stands out because the Republicans are the Stepford party.
But has he been speaking out against Trump consistently? No. Has he argued against or voted against Trump policies (with the exception of his ACA repeal vote)? No. Is he urging others in his party to oppose Trump? No. Is he going to leave the Republican Party? No.
McCain is not acting as a statesman, let alone an ally. He is just an old man trying to get into heaven, or at least secure a better spot in the history books.