So what does the term mean?
The first thing to understand is that the term is almost entirely used as a racial slur. Nobody calls himself a "white supremacist".
If you define the term as someone who advocates the political supremacy of the White race over non-whites, then it is almost impossible to find anyone who matches that definition. It is easier to find Jewish supremacists, or Black supremacists, or Chinese supremacists.
The term is almost entirely used by the anti-racist left, and they use the term to mean all White people. They consider Joe Biden to be a White supremacist, as they are especially contemptuous of White who claim to be not racist.
Biden himself just used the term to refer to a 17-year-old Illinois boy, just because he is White and supported the police.
In the debate, Biden asked Trump to condemn White supremacists, and Trump said "Sure". Then Biden asked him to tell them to "stand down", and Trump said "Sure" again. Then Biden asked Trump to specifically ask the Proud Boys to stand down, and Trump did that also. But when Trump brought up the threat from Antifa, Biden refused to condemn Antifa, saying "Antifa is an idea, not an organization."
When Blacks complain about White supremacy, they usually talk about slavery or Emmett Till or some other issue that no one alive can relate to.
When Jews complain about White supremacy, it is often about a handful of protesters at a Charlottesville 2017 rally who chanted "Jews will not replace us." The chant referred to Jews advocating immigration programs to replace Americans with non-whites.
I haven't seen dozens of Jewish articles complain about that Charlottesville rally, but none of them deny that Jews seek immigration of non-whites to replace Americans. In fact they all seem to advocate a form of Jewish supremacy, where Jews cannot be criticized for their anti-White policies.
Pres. Trump is probably the least racist President we have had in a long time. All this Jewish talk of White supremacy is just code for other Jewish policy goals.
Update: Orthodox Jewish commentator Ben Shapiro aften attacks Trump and White supremacy, and he has a good video demonstrating that Trump repeatedly denounced White supremacy in the debate.
Obviously something else is going on here, when so many in the news media say just the opposite of what happened. One explanation is that they are Jewish supremacists.
Update: Ann Coulter explains the Proud Boys. They are not White supremacists -- they are not even White!