To get a better sense of Trump's wild accusations of the "Commie" Democrats, a US acquaintance wrote:
"Bear in mind when Republicans throw around accusations of a Democrat being a “commie” is that virtually all politicians here are rather more right wing than any left leaning politician in the UK,
and the Democrats as a whole would probably fit between the Lib Dem’s and the Conservatives in the UK.
There are outliers, eg the so-called Squad of progressive Democrats, and Elizabeth Warren, who are more to the left, but, to be honest, even they would probably fit on the more moderate end of the Labour Party.
There’s good old Bernie Saunders, of course, who is truly left wing - he’s also not actually a Democrat, although he votes with them - but if you picked up the rest of the party ......they would probably find their home among those parties which would be described as centre -right.