First, why did it take almost three weeks for Trump to do something about Flynn? That question still lingers, and deserves an answer.
Second, although it took even longer for Nixon to throw his underlings under the bus, he eventually did. It didn’t help.
Third, it’s true that Obama waited until after the election until retaliating against the Russians. There are a number of possible reasons for this, including yours, but one very plausible one was to keep the election as neutral as possible without Russia dominating all the news.
Fourth, if Hillary had won, would I still want an investigation into whether or not Trump or his team colluded with the Russians to undermine our election? You bet. I would also want an investigation if the tables were turned and Hillary was the one Russia helped.