Trump disputes the Intelligence Agencies conclusions for two reason. First, it is bad for his ego for someone to suggest that he had help in winning the election. Second, if he follows through with his ideas of recognizing the Russian acquisition of Crimea and removing sanctions on Russia, he would appear to be rewarding Putin for his help. As to whether it affected the election, it is important to remember how close it was. Trump won Pennsylvania and Wisconsin by only 0.7% and Michigan by only 0.2%. If these 3 states, with their total of 46 electoral college votes had gone to Clinton, she would be President-Elect. In view of the one-sided intervention, it is not only possible  but probable that the steady drip-drip  of embarrassing information from July to November cost Clinton sufficient votes in those states to give the election to Trump. However, neither result would have satisfird me since I regarded both of them as totally unfit to be President.