In an urgent memo to the field of G.O.P. Presidential candidates, the Republican National Committee chairman, Reince Priebus, praised them for their relentless personal attacks on Hillary Clinton, but warned that their hatred for the former Secretary of State might be peaking too early. Priebus called the candidates ongoing evisceration of Clinton magnificent, but expressed his concern that no human beings, even an impressive group like yourselves, could possibly sustain such a high intensity of throbbing hatred for an entire year and a half. Remember, this is a marathon, not a sprint, he wrote. You need to leave some hate in the tank. In the conclusion of his memo, Priebus advised the candidates to take an occasional day off from hating Clinton so that they could return to despising her with renewed freshness and vigor. Responding to the R.N.C. directive, Sen. Ted Cruz (R-Texas) said that he understood Priebuss concerns, but assured him that, at the end of the day, they were groundless. Anyone who doesnt think Im capable of spewing an infinite stream of vitriol and bile doesnt know what Im made of, he said, pointing with pride to his long record of hating President Obama. 