During his presidency, Truman faced significant challenges in advancing comprehensive civil rights legislation. While he did make some notable steps, such as desegregating the armed forces in 1948 and advocating for civil rights, a comprehensive civil rights bill that would have established extensive legal protections against racial discrimination was met with strong opposition from Southern Democrats and some Republicans. These political barriers hindered Truman's ability to deliver on his ambitious agenda for civil rights, making it a central domestic initiative that remained unfulfilled.
In contrast, the other options do not align as closely with the significant barriers Truman faced. The development of new transportation systems fell largely under state and local government responsibilities as well as private enterprises rather than a direct initiative during his administration. An increase in military personnel was not a prominent focus, especially after the scaling down of forces following World War II. Expansion of the New Deal programs also faced considerable opposition, both politically and socially, as there was a shift in the country's economic focus following the war and a move toward more conservative fiscal policies, making the civil rights initiative a standout area where Truman's efforts fell short.