Left-wing can be relative to the nation. The most meaningful faction of American "left" is the Democratic Party. The global definition is based on socialist vs capitalist ideological splits, in which all forms of ideological liberalism are right wing or, in the case of social democracy, arguably what centrist actually means.
The Democratic Party is therefore left-wing internally and right-wing globally, thus people saying "America does not have a left wing."
Leftists are socialists. It is not relative. Democrats are not leftists. Bernie Sanders is, as a democratic socialist. You are not "An American leftist" because you like billionaires existing but don't want to genocide brown and gay people. That's just liberalism as it is supposed to be.
This is also why a leftist would deny that "liberalism" is left wing. Liberalism is a broad ideological judgement and can be assumed to be using the global standards as a result, America does not have sole claim to defining it. So American liberals are the American left, but liberalism itself is right-wing.
This really isn't that complicated if you know the basic meanings of the words in question, which is why liberals find it so confusing. Liberalism is the status quo position of the American electorate and moving beyond it requires education while going along with the binary party politics does not.
Edit: this was supposed to be a response to the first comment instead of me telling OP things they already know
Remember the poem? 'First they came for the communists'. They never came for the liberals, they worked with them. There has always been a difference, and there will always be a difference.
See the problem with this stupid labeling is that everyone has a different definition so no one knows what the fuck anyone else is saying. Just knock it off with the labels, attribute the quality or idea you mean instead of a lazy fucking label...
You know how many conversations Ive been in where i was confused until i realized the word meant different things to us. Seriously the labeling in politics is getting out of control, everyone groups everything up into a category because it makes it easy to manipulate people against it, so noone knows what the word means anymore because everyone is defining it as something different every day.
It wasn't until Ron Paul was running for office that I learned that "liberal" was mostly used as a shorthand for "libertarian" and what a libertarian was. Before that I thought it just was a synonym for progressives/democrats. They're not left-wing. They're just not as far right as a fascist.
So this election was lost hard because of infighting and the resulting apathy so great thanks for adding more infighting by shitting on the inferior "liberals"
Unconstrained campaign financing and lobbying will always dilute the power of democracy and liberalism, but liberalism is a good alternative to bloody revolutions or forced changes. Humanist philosophies prefer liberalism to some degree, but I could be wrong 🤷♀️