Some policies embraced by the Populist left, not only the DSA, include "Medicare for all" and "paid family leave", which are overwhelmingly popular with "We The People".

Oh, I agree. But other DSA positions are very much rejected by most US voters.
Example:
program.dsausa.org: DSA Program - Workers Deserve More!

Legalize migration, grant amnesty for all immigrants regardless of status, provide a path to citizenship for all permanent residents, and end visa caps and quotas.

We could debate these policies here, but your average voter is NOT for this. Did we learn nothing from the 2021-2022 debacle at the border and Trump's subsequent win? Look at Western Europe. A policy of unchecked migration is not a vote winner. You can't help people if you have no power.

"defund ICE" or "defund the police", as offered before, is crazy talk. But those agencies need to get rid of the storm trooper tactics. It should be obvious that it is wrong to sit on a man, until he slowly suffocates. It should be obvious that it is wrong to grab brown people off the street and rough them up. I agree the border should be secure. I agree that "JCs" that cheat USians by hiring illegals, should face consequences. But the way policy is being implemented is wrong.

Abso-fucking-lutely. 101%.

And if Third Way has it's way, by sabotaging Dems, because they were a little farther out on the spectrum, we get unfettered GOP nutter rule.

Seems to me they don't want to sabotage dems, they want to promote dem candidates that agree with The Third Way.
Seems to me that such dems might be in a better position to win elections in swing states. But then I tend to agree with The Third Way.
I'm a socially liberal capitalist (with regulation).

For one issue, like many immigrants I've seen what happens when a government takes over "essential industries". Just consider the British car industry. A disaster.

Background: I was at college during the miner's strike:
en.wikipedia.org - United Kingdom strike

From 1984 until 1985, a major miners' strike shook the British coal industry in response to proposed closures of uneconomic pits. It was led by Arthur Scargill of the National Union of Mineworkers (NUM) against the National Coal Board (NCB), a government agency. Opposition to the strike was led by Margaret Thatcher's Conservative government, which wanted to reduce trade union power.

My college was a hotbed of socialist protest against Thatcher and for the miners. I could and did sympathize with them, enough to sometimes contribute a bit of money I couldn't afford, but come on, digging coal we didn't need from miles underground. Stupid.