We were on the OFF RAMP but someone that Trump unnecessarily denigrated voted to spite Trump and force US back on the Highway of Socialism.
Bingo.
That doesn't excuse what McCain did. If he was running for reelection, that would deservedly sink him.
But just because McCain was petty and vindictive doesn't excuse Trump. Trump deliberately antagonized someone he knew to be petty and vindictive, either because of Trump's own sheer stupidity, lack of self-control, or because he simply didn't care about the consequences because he thinks public insults are "funny".
Regardless, between the two of them, they killed the repeal of most of Obamacare. And Trump is the one running for reelection now, so....