There are many, many reasons. Trump promised to be extra soft on Russia re:NATO, re:Ukraine, etc. His single contribution to the GOP platform was to soften th

There are many, many reasons. Trump promised to be extra soft on Russia re:NATO, re:Ukraine, etc. His single contribution to the GOP platform was to soften the GOP's position on Ukraine. Some of his staff were also Russian clients. He's also expressed open admiration of Putin and Putin's style of governance, and emphasized that he wants the US to get along with Russia. His son secretly met with Russian reps before the election to discuss US policy in Syria and elsewhere. A Trump win would give Russia tremendously greater influence over Europe. Given Putin's open assistance to Trump in the election Trump would owe Putin favors, and it's likely one of the favors Russia would pursue wold be lightening the massive sanctions Clinton imposed on Trump. Trump's also incredibly easily manipulated which certainly serves Russia's interests.