We live in a world of perception.
It is much less a story if the other candidate wins, meaning that the Russians committed cyber warfare against us, but the Americans rejected their sabatoge.
But, our story is that Russians pulled it off. Hence, it becomes irrelevant whether or not Trump would have prevailed anyway. We'll never know.
So, it taints President Trump's legitimacy as the true and rightful winner. We don't want tainted elections, whether or not the taint is real or just perception.
We want clean elections, so the victor can govern, without lingering controversy.
Trump is the victim of Russia's cyber warfare, not Hillary, not the Democrats.