You're assuming the disease is an absence of character; it is not.

The present US system is split-everything-into-districts then winner-take-all-in-each-district. This system is known to have a mathematical fixed point (as a transformation polity → polity) where:

- There are two parties who evenly divide political power.

- Those parties are deadlocked 50/50 and therefore very little gets done.

- Those parties are spineless—they do not stick to whatever “core principles” they might have a reputation for, and an issue which party A champions one decade might become party B's forte a few decades later.

- Few people actually consider themselves a part of either party; the substantial majority considers themselves “independent” voters—but they would admit under pressure that they do mostly vote for one party consistently. If asked why they don’t consider themselves a part of that party they will indicate that more than half of what “their” party does, they do not support.

- The crux is why they don’t vote for the “other guys” which comes down to being appalled and terrified at some of what the other party stands for.

The core features of the disease all interrelate. The spinelessness is being used by the two parties to find an issue which the other party does not seem to care about, in order to demonize the members of that party. For example, witness Tucker Carlson talking this year about the risk of fraud with mail-in votes; the subtext is that Democrats because they do not care about this topic are displaying a core moral lapse—they are too trusting, perhaps too enamored of past studies of voter fraud—which will dangerously cause the demise of the sanctity of our elections if everyone starts doing this mail-in voting this year in response to the pandemic. This “what the F--- are they thinking” mindset that riddles your comment towards them, is pointed right at you by that other half of the country.

The reason it has to be this way is that literally having a spine is a political death sentence. It’s economics and incentives. We had a party which tried to have a spine, “we don’t care about slavery one way or the other, we have always been about TARIFFS and that is what we are going to talk about this election cycle!” They were called the Whigs and meanwhile a party which expertly played the demonize-and-win game emerged under Abraham Lincoln, and the Whigs just kind of faded over one or two election cycles into obscurity as the US civil war took its toll.

Oh, yeah, that's the other thing. Constantly demonizing the other party doesn't work forever; this "district-and-winner-take-all" approach leads to civil war. But the point is that the cause is not that the other 50% of the country is morally reprehensible; the cause is that it is in each party's best interests to paint the other 50% as morally reprehensible. This in turn comes from the fact that the winner-take-all nature of the election makes it really hard to fork a political party; witness e.g. the recent emergence of the “Tea Party”—but never as an actual political party as that would be suicide to their desired goals.

The easiest solution to implement right now would probably be to make every state into one big multi-member House district running a party-proportionate election. It is not clear what would happen to the Senate under such a structure, but it seems plausible that the US would fragment into 5 or 6 political parties and Senate candidates would court the endorsement of 2 or 3 of them. But it is possible that the Senate would still be 50% Democrat, 50% Republican even as the House lost those particular affiliations. But at least something would be moving forward.