The Communist Party teamed up with the AFL-CIO in a demonstration last month in Washington, according to Accuracy in Media.
The CPUSA was an “endorsing organization” of the "One Nation March" and was given space to set up a literature table by the rally organizers, reports AIM's Cliff Kincaid, whose article is found here:
A two-page official list of the rally's organizations, Kincaid says, shows that the party was given a “reserved space.”
"The officially-sanctioned groups also included the AFL-CIO and several left-wing labor unions; United for Peace and Justice, founded by veteran Marxist activist Leslie Cagan; Code Pink; the ANSWER Coalition, a front of the Party for Socialism and Liberation; the League of United Latin American Citizens (LULAC); the Committees of Correspondence for Democracy and Socialism; Green for All, the group once associated with former White House official Van Jones; Democratic Socialists of America, which helped give Barack Obama his start in Illinois state politics; and the NAACP."
The Communists' participation in this rally was for the most part concealed by mainstream media.
The Communists have been very cagey about their take on who was behind the 9/11 attacks. Those on the hard left have generally been opposed to looking into the probability of conspiracy.
A few minutes ago, I tried checking the CPUSA web site to get some idea but all my searches -- inlcuding one with the single keyword "9/11" -- drew blanks.