Final answer:
Ralph Nader became nationally prominent for his work in consumer protection, later expanding his focus to social justice and environmental issues, influencing the political landscape significantly.
Step-by-step explanation:
Ralph Nader rose to national prominence on the issue of consumer protection and later became known for his environmental activism. Nader first gained attention with the publication of his book 'Unsafe at Any Speed' in 1965 which criticized the safety record of American automobile manufacturers and led to significant reforms in auto safety standards. Later in his career, as he ran for presidency, Nader's focus expanded to include a broader range of social justice and environmental issues. Despite running as an independent in 2008 and as the Green Party candidate in 2000, some analysts suggest that his campaigns, especially in 2000, drew votes from Democrats and potentially affected the outcome of the election. Nader's legacy today is intertwined with his environmental activism, a cause that has earned him recognition including the 2007 Nobel Peace Prize awarded to Al Gore, whom he arguably impacted in the 2000 election.