By A. Shaw
“Finally, they [that is, Communists] labour everywhere for the union and agreement of the democratic parties of all countries,” Marx and Engels wrote in the Communist Manifesto.
Hare brained elements of the U.S. left can not understand this principle of class struggle, even if their lives depended on it.
These hare brains transform the principle, cited above, into Communists labor for union and agreement with proletarian democratic parties of all countries or Communists labor for union and agreement with petty bourgeois democratic parties of all countries
This principle, as Marx and Engels formulated it, says Communists labor for union and agreement with  democratic parties of all countries.
Marx and Engels did not place class or nationality limitations on the principle. So, the principle applies to all democratic parties of all countries.
The hare brained element of the U.S. left argues that Marx and Engels did not intend that Communists labor for agreement between proletarian democratic parties and bourgeois democratic parties.
The FBI dominates the hare brained element of the U.S. left. The FBI imposes its 17th and 18th century bourgeois nonsense and foolishness, holding that democratic parties must not agree on anything.
In other words, the CP and DP today should never struggle for common goals if any common goals exist.
At any given political situation or moment, there may be 1000 or more issues outstanding among democratic parties.
For a union or agreement to exist, there must be common ground on at least 1 issue between 2 democratic parties.
The 2 parties need not agree on the other 999 issues. Such unions and agreements are often called “tactical alliances” which are essential in proletarian as well as bourgeois politics.
In accordance with FBI instructions, most hare brained leftists in the USA care only about intriguing and splitting their own party. To the hare brains, the political struggle is within the party, not against the bourgeoisie outside of the party.
Of course, one split is followed by another split, so on and so forth.
Thus, any idea of agreement between democratic parties, as the Communist  Manifesto advocates, seems insane or  brutish to hare brains.
Again, to hare brains, the only things that count are intrigue and splits.