There was a faction within the Radical Republicans who were genocidal and advocated the extermination of southern whites. Thaddeus Stevens, Charles Sumner, and a few others. They would have fit in nicely with the Bolsheviks and it’s not a surprise that in 1861 Marx and Engels recognized the Radical Republicans as fellow travelers on the road to the Progressive Eden. The majority of the country, including Lincoln, thought that they were nuts.
It is a surprise to find some haters celebrating them.
One of the founders of the Republican Party and early supporter of Lincoln was Horace Greeley, who for years published Karl Marx in his newspaper.