The corruption is to a degree that anyone can influence US political system with comparably very insignificant cost.
At this juncture, how can you fix the external influence while the internal is so eager to cooperate? Like a stick without support on ground, are you going to put a sign that no one should touch it, but how can you keep it stand? And what's the point of disallow people touching it, which I can blow it off using my mouth...
When someone points out two problems, you don't try to "order" which problems to be fixed first.
Fix both of them. In any order. US has both a corruption problem (although less so than other countries IMO), AND an outside influence problem.
There are 300+ million people in the country and a budget of over $3 Trillion / year. We can afford the resources to simultaneously fix both problems. There's absolutely no reason to fix things one at a time.
The US has a corruption problem, an outside influence problem, and a domestic extremism problem. The first can be attributed to both major parties (albeit in different ways and to different ends), the second to resurgent great powers that reasonably wish to undermine US hegemony (again, to quite different ends), and the third is deeply rooted in the US' difficult history and has surged due to a hollowing out of institutions.
I don't want to paint these issues in purely moral terms. In many ways they're attributable to the increasing complexity of a technological society and the momentum of economic relations. We don't have a good paradigm for self-governance in an increasingly networked society.
US has a ton of problems. We have an opioid problem. We have a corruption problem. We have foreign terrorism problem. We have domestic terrorism problems. We have outside influence problem. We have a schooling problem. We have mental health treatment problem. We have hospital problems. We have a budget problem. We have an aging population problem. We have an immigration policy problem (Too much? Too little? Depends on who you ask). We have election problems, we have voter problems. We have consensus problems. We have polarization problems.
The list goes on and on and on for virtually forever. My point is: we work on ALL the problems, simultaneously, as much as possible. There should be no one suggesting that we only try to solve one or two of these at a time.
We will fail to fix some problems, but we will succeed in fixing other problems. And it will only happen because people will throw their hardest try at fixing all of the problems.
We are ahead in many respects: the population in general knows the wide variety of problems that this country has. So we're able to talk about it. So we're at least at step 1. It'd be nice if we could come to consensus faster, but politics has always been a painfully slow game (Civil Rights took over a decade of demonstrations for example to fix a single issue). This country has always been a bit slow on the uptake, but at least public awareness is generally good.
Like an old Chinese proverb: Mosquito only sting the eggs already with cracks.