The correct answer is A) highlighting his opposition to the Taft-Hartley Act.
Prior to the 1948 campaign, Truman won back the support of labor workers by highlighting his opposition to the Taft-Hartley Act.
The Taft-Hartley Act or Labor Management Relations Act was a Federal law of 1947 that prohibits some union practices and forces unions to disclose financial and political activities. That measure did not like the unions and workers were in opposition to the Act. They called the “slave-labor bill.” That is why Truman before the campaign of 1948, won back the support of labor workers by highlighting his opposition to the Taft-Hartley Act.
The other options of the question were, b) supporting of the passage of the National Security Act, c) pushing for equal rights for African American citizens, and d) opposing to strikes of railroad workers.