Then what is the best measure at this time and why is it better than polling?
Evaluate the kinds of attacks that are likely to be used.
Evaluate how people react to those kind of attacks. You can use polls for that.
Here are some Gallup Polls one can use to argue people accept socialism.
But you can't stop there.
538: Who would Americans NOT vote for in 2015?
Of all the characteristics a voter would not vote for, "socialist" topped the list, above atheist and muslim. Again, putting a positive spin on that:
Now, this polling took place shortly after Sanders’s 2016 campaign got started, so it’s possible that attitudes have shifted since then — after all, three socialist candidates ran for Congress in the 2018 midterm elections and won. Nonetheless, an August 2018 survey from YouGov found that 41 percent of Democrats and 29 percent of independents said they would feel “enthusiastic” about or “comfortable” with “a candidate for president who described themselves as a socialist,” while 59 percent of Democrats and 71 percent of independents said they would have “some reservations” or would feel “very uncomfortable.” These numbers suggest that there is still an opportunity for Trump to score points by painting his opponent as a socialist in 2020, which in addition to revving up Republicans may also undermine the cohesion that Democrats and independents have built on anti-Trump sentiment.
You think the Trumpers can't make Sanders out to be scary?
There are clips of him promoting or speaking positively of Castro and the Sandinistas. Of him saying the government should take over businesses to address climate change. Of him saying the government should fund all health care and whatever else. When asked how that would be accomplished, his answer is, our country is rich enough, people would really pay less, blah blah blah.
Those things are just the tip of the iceberg and can be exploited with millions of dollars to sound radical, crazy, scary, and Sanders is an easy target for these attacks.
Just because a fair number of young people are enthusiastic about such a country, more people than that are easily scared away by radical changes like that.
There is a long history of the US population NOT voting for radical change.
People will think their taxes will go through the roof and Sanders is so bent on his ideological argument,
he cannot make a common-man case for it. He hasn't yet. He only makes the anti-capitalist case he's been making since he was a young man, the country is rich so the citizens should benefit.
That's not how this country sees itself. It sees itself as a rags to riches country.
This election is too important to risk that. Trump is dangerous and we are seeing that in how he's responding to the virus crisis.
But he pulls the wool over his cult followers by signing an agreement with the Taliban (good luck if you are female or any religion but radical Muslim in Afghanistan), and calling a bunch of vaccine developers to a photo op with him in the White House. He blames the stock market crash on a plot against him by the news media—more anti-science stupidity. Suppress bad information, throw some stats about a couple million masks out there as if that's all we need.
Just wait until he closes the Mexican border if you want to see how fast a long term recession will emerge.
I don't want to take that gamble. You would have this vote be between two extremes and one side is better at conning voters.
There is an almost as bad slew of attacks waiting for Biden. I'm not happy about that option either. But the Sanders gamble is much riskier.