A big tent... that speaks with one voice...

He said if “a big tent movement” could be created “that speaks with one voice, does the necessary research to know exactly what messages need to be conveyed in a consistent way, then we might just have a chance to shift the dial in the next few months. That is what is needed and time is tremendously short.” (The Guardian.)

Is a noun phrase "a big tent movement” that speaks with one voice, does the necessary research to know exactly what messages need to be conveyed in a consistent way an antecedent ofThat in That is what is needed in the passage above?

Is what is needed a relative clause adjectivally complementing That inThat is what is needed?