I do not have any problem at all with that - in fact I applaud him for it.
For years we have watched democrats disrespect republicans (and conservatives) in the most vile, hateful ways while republicans have tried to ignore it.
Republicans generally respond by pretending that democrats are just regular gentlemen and ladies and act as if the most hateful treatment by democrats is perfectly acceptable.
One example: Democrats trashed George "Dubya" Bush and stabbed him in the back for 8 years in spite of him trying to "reach across the aisle".
Yet he did little or nothing in reponse or to counter their behavior.
Finally we have a president who does not pretend that his enemies are his good friends.
Nor does he pretend that their disgusting behavior toward him and his family is within acceptable boundaries.
That is why president Trump has good reason to boycott the annual White House Correspondents' dinner and why he has good reason to snub hate mongers like Blitzer and Tapper.
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I used to get upset when Bush let the lies go unanswered. Remember the British lost the revolutionary war because they followed gentleman’s rules of war.