how do you approach and sell the idea that this nation and its system cant be salvaged

You're not going to be able to convince someone in a single conversation. You must first plant the seed of doubt in their mind.

Attack the idea that America is a democracy. If America isn't a democracy, it can't be reformed through democratic means.

Start with the obvious things, like the electoral college, misapportioning of senators(1 voter in Wyoming has the same representation in Senate as 59 people in California), the two party system. The power of money, lobbying, etc. Talk about the ideas that have long had broad support, but aren't being dealt with, taxing the rich and big corporations, like modest gun reforms, dealing with political corruption, codifying roe v wade, etc.

Edit: You won't get there in one discussion, but you can plant the seed.

Get them into an organization, politically educate them, and let them observe the outcomes of their attempts to take action against the system. Make them be honest and critical about what is accomplished. Basically, I think the major contributors are inexperience, unfamiliarity with history and theory, and not testing their ideas honestly (they are idealistic).

Selling the idea of literally destorying the current state of society is hard. I'd be interested to know too.

The chronic crisis of American democracy: the way is shut by Benjamin Studebaker goes in depth on how every political movement from Bernie to Trump is structurally incapable of making any meaningful positive reforms to the American system. The book is also a bit cynical on the efficacy of revolution but if you want to convince someone that the system is unsalvageable this is the book for you

A good seed you can plant is by pointing out that in all the countries that "followed our example" by moving from monarchy to democracy basically nobody did it like we did it. Even the countries the USA had complete control over like Japan after WW2. Nobody looks at our broken-as-shit system and says "heck yeah let's do it that way!" Other systems and governments are rife with counter-democratic structures and corruptions unique to their own situations of course, but the whole world had our system as a possible inspiration and said "ehhh not like that." That refusal has happened hundreds of times in hundreds of countries.

Start by chipping away at the parts of American exceptionalism like that. Plant seeds of doubt.

tell them the story of john brown

I ask myself this question every day but I can't think of a single answer to it

Sorry I couldn't be helpful, but it is an important question

Unless they are completely irredeemable, you can probably find some policy issue or local "problem" that could be easily fixed with direct governmental effort that everybody seems to agree with but that never gets on any ballot or is stopped by a few members of the local governing body who never seem to be convinced by the majority of people to move forward with the project.

(being USA-centric with this example)

Hey, did you know that Single Payer Medicare for All is a super popular policy? It always polls super well, in every state and every demographic. How is it that the issue never shows up for the people to vote on? How is it that politicians can't seem to enact the will of the people?

I wonder why that is? Lets talk about it...

If I had to try to break it down simply to get libs across the line, or at least onto the fence, I'd try to go if > then statements that seek agreement, then push into the next line of argument. Something like:

Putting it under spoiler tag cos it's a bit long, maybe even self indulgent:

do they care about other people or the environment? the case for like morally needing to be punished for its crimes (re marginalized people in the US, or internationally )or the primacy of oil interests destroying the planet are more to the point than explaining theories of parliamentary organization & class rule

Explain how the two parties are bad. Then explain why lobbying causes them to be bad, and the electoral system keeps them in power regardless. Finally, explain how, obviously, none of the two parties will remove either problem, and therefore the system must be destroyed. Bonus if they also agree that capitalism must end.

they've been saying that since 1776 and it hasn't worked out yet. face it, she's a lemon. if you want salvage, take her to the junkyard.

you can't, people are cattle, and can only understand things thru vibes-based herd reasoning

you have to appeal to the and say stuff like "why the fuck is China so ahead of us?"

Additional ammo: 'if Trump is an existential threat to the system... What use is the system if it allowed him in?'

Also, point out the idea of how the economy is this nebulous thing, that just so happens to have an effect like a god on every facet of our lives. This is a fact that nobody can deny. When they acknowledge this, simply ask them "did you vote on for this economy?". Of course not, you don't get to, but it - a man made thing - gets to determine your life course. Then point out that famous rich people can sway the economy with their words as they please. If Musk called a press conference in an hour (you, me, and everyone we've ever known doesn't have that ability.) and said money isn't real, it's all a big scam, bla bla bla, world markets would collapse and you'd probably lose your home.

That John Brown was the one good white man; and that odds are good if he was with us today, he'd have shot every single one of us, communists and supposed-leftists alike, for allowing the carceral slavery complex to exist and perpetuate as it has.

Start with local issues they can actually relate to.

In my experience, it's often privileged leftists who have a "burn it all to the ground and build something better" mindset come from a place of privilege that would enable them to weather the storm. It reminds me of men telling women right now "things have to get worse before they can get better" or "it doesn't matter who wins" when policies relating to bodily autonomy are critical to women.