BY JOE CONASON As soon as Donald Trump brayed that John McCain is “not a war hero” and went on to mock his suffering in North Vietnamese captivity, the righteous reaction of Republicans was entirely predictable. Nearly every would-be presidential candidate in the GOP immediately sought to wrap the loud-mouthed celebrity’s gaffe around his neck. The incident presented an irresistible opportunity for Trump’s rivals to stoke public indignation against a merciless, infuriating, suddenly formidable opponent. […]