fellow traveler
noun
                                
              
          
                                                      : a person who sympathizes with and often furthers the ideals and program of an organized group (such as the Communist party) without membership in the group or regular participation in its activities                                      
                
                                
            broadly                
          
                                                      : a sympathetic supporter of another's cause                                      
            
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  Merriam-Webster unabridged




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