Yeah. There are two main reasons why they will donate to both parties. One like you said is to make sure whoever wins they still have influence with. The other is that it raises the threshold needed to be competitive in an election. If you DON'T do what the donors want, you lose that funding and have to compete with the ones they are still backing. It makes it absurdly difficult to run insurgent campaigns. The recent electoral successes took a national effort on the part of US leftists to make happen in order to just secure a handful of seats. You need a lot of engaged people to go up against people who can casually drop tens of millions of dollars to blast the airwaves with ads.