The Philadelphia Inquirer has this story, which is mostly about Professor Jerome Segal, founder of the Bread & Roses Party. That party is on the ballot in Maryland, but nowhere else. Segal expresses the opinion that the Green Party and parties with similar ideas should not run for president in 2020 in swing states.
There is considerable evidence that left parties do not hurt the Democratic Party, but none of it is mentioned in the story. (1) political science research presented in “The Future of American Poilitics”, a 1950 book by Samuel Lubell, showed that Harry Truman would have lost to Thomas Dewey without the Progressive Party candidacy of Henry Wallace; (2) detailed poll analysis and election returns analysis from 2004 showed that Ralph Nader voters were more likely to vote for George W. Bush than John Kerry if Nader hadn’t been on the ballot; (3) the book “Predictably Irrational” by Dan Ariely presents psychological experiments that show if three choices are available, and two of them are similar but one of the similar choices if clearly superior to the other, then that superior choice gains, versus the choice that is not similar; (4) the Communist Party in 1936 determined that they wanted Franklin Roosevelt to be re-elected and they facilitated that by running their own nominee, who used his attention in the public forum to encourage the defeat of the Republican nominee, Alf Landon.