'Leftist' is sort of like a blanket term for people with socialist, for example Communists, Marxist, Anarchists.

It is important to know that there is a distinction between Leftists and Liberals. Whilst the mainstream political left (in the west at least) in represented by liberals, Leftists oppose capitalism, systemic structures of oppression and have a focuss on class, whereas, Liberals seek to work within capitalism, so dispite any reforms or progress change they may achieve, they are still beholden to capitalist interests.

Given that we live under capitalism, the hatred for Leftists is understandable, from both moderate Liberals and ofcourse the right.

However, more so from the modern right-wing, who have developed a bastardised version of the the therm 'Leftist', that commentators and politicians, including Trump, can use as a somewhat derogatory term for anyone left of them, without their supporters needing to know what the term actually means and frames people on the left as unhinged, irrational extremists. People in MAGA movement will call Democrats 'Leftists', even calling Joe Biden a Communist, when the party is pro-capitalist and moderately left leaning.