Trump crossed lines in the depth of his attacks on McCain - he made it personal, as he does all the time. And his supporters cheer it.
GMAB, TRUMP's comments were in response to McCain attacking TRUMP and his supporters. How many times did Obama cross the line during the 2008 campaign, yet McCain was able to get past the petty attacks from Obama.
I voted for McCain and he lost, perhaps had he gone after Obama with the same amount of vitriol as he has for TRUMP he would have won.
TRUMP won because he along with millions of others who voted for him understood playing nice politics losses elections. So while people like McCain are hung up because of petty comments made during a contentious campaign, TRUMP moves on beyond words with actions.
In war collateral damages are often accepted because the intention of outcome is for the greater good, If McCain was able to accept the collateral deaths caused by the war in Iraq to serve the greater good, he should have been able to get over simple words from TRUMP to serve the greater good for the US.