Use stream of consciousness to answer the following. A bill to accord national recognition of the holiday was introduced in Congress in 1913. In 1916, President Woodrow Wilson went to Spokane to speak at a Father's Day celebration and he wanted to make it an officially recognized federal holiday, but Congress resisted, fearing that it would become commercialized. US President Calvin Coolidge recommended in 1924 that the day be observed throughout the entire nation, but he stopped short at issuing a national proclamation. Two earlier attempts to formally recognize the holiday had been defeated by Congress. In 1957, Maine Senator Margaret Chase Smith wrote a Father's Day proposal accusing Congress of ignoring fathers for 40 years while honoring mothers, thus "(singling) out just one of our two parents". In 1966, President Lyndon B. Johnson issued the first presidential proclamation honoring fathers, designating the third Sunday in June as Father's Day. Six years later, the day was made a permanent national holiday when President Richard Nixon signed it into law in 1972.

Answer this question based on the passage: when did father's day become a national holiday?
To answer the above question, the relevant sentence is: Six years later, the day was made a permanent national holiday when President Richard Nixon signed it into law in 1972. Final answer: 1972.