Having evidence that the fears are based in reality and proposed policies that would help said people is a point for the latter, obvious contradictions in those one for the former.
Proposed policies being realistic vs vague broad strokes that are unlikely to be legal to implement would be another indicative axis.
I suspect that having "obvious contradictions" in policies is an extremely high bar for modern political groupings generally - ie all political parties and their leaders are populist now.
I think that populism has an element of "tear the system down", which is something that goes considerably further than the usual "throw those bums out".
When Biden ran against Trump, he tried to appeal to voters who were unhappy with Trump, but nobody called him a populist. He was just a normal politician. Trump isn't. Neither is Bernie Sanders.
How do you decide? I can't give you a clear answer there. Still, there is a difference. (Maybe "do they talk like a normal politician"?) Most out-of-office politicians are on the Biden side; only a few are on the Trump/Sanders side.
If by "tear the system down" you mean anti-establishment and anti-elite, I agree. That's an essential component of populism.
I don't think many people would say Biden was anti-establishment. In 2020, Trump hadn't been in office long enough to change the establishment very much.
> Most out-of-office politicians are on the Biden side; only a few are on the Trump/Sanders side.
At least on the GOP side, it’s because they care only about cheap labor. Free trade to harness cheap labor abroad, and mass immigration to harness cheap labor for what can’t be outsourced.
How do you decide if they are "pandering to discontent and fear of some portion of the populace" or "standing up for neglected people"?