The phrase "the legions of the concerned and committed" is part of Nixon's first speech as president of the republic. He uses this phrase to refer to American citizens who are essential to the country's political, economic and social progress, along with all the rulers, including the president. That's because American citizens were people concerned about their homeland and committed to its success. With that, he reaffirms the need to work together with the people, to be a good president.
