Article: The race was the most expensive for Congress in the country that year and four days before the general election, Durkin withdrew and endorsed Cronin, hoping to see Kerry defeated. The week before, a poll had put Kerry 10 points ahead of Cronin, with Dukin on 13%. In the final days of the campaign, Kerry sensed that it was "slipping away" and Cronin emerged victorious by 110,970 votes (53.45%) to Kerry's 92,847 (44.72%). After his defeat, Kerry lamented in a letter to supporters that "for two solid weeks, [The Sun] called me un-American, New Left antiwar agitator, unpatriotic, and labeled me every other 'un-' and 'anti-' that they could find. It's hard to believe that one newspaper could be so powerful, but they were." He later felt that his failure to respond directly to The Sun's attacks cost him the race.

Now answer this question: What did Kerry think cost him the race against Cronin?
his failure to respond directly to The Sun's attacks