Roosevelt's plan to convince Hoover to run for the Democratic nomination fell through after Hoover publicly declared himself to be a Republican, but Roosevelt nonetheless decided to seek the 1920 vice presidential nomination.
After Governor James M. Cox of Ohio won the party's presidential nomination at the 1920 Democratic National Convention, he chose Roosevelt as his running mate, and the party formally nominated Roosevelt by acclamation.
Although his nomination surprised most people, Roosevelt balanced the ticket as a moderate, a Wilsonian, and a prohibitionist with a famous name.
Roosevelt had just turned 38, four years younger than Theodore had been when he received the same nomination from his party.
Roosevelt resigned as Assistant Secretary of the Navy after the Democratic convention and campaigned across the nation for the Cox–Roosevelt ticket.

During the campaign, Cox and Roosevelt defended the Wilson administration and the League of Nations, both of which were unpopular in 1920.
Roosevelt personally supported U.S. membership in the League of Nations, but, unlike Wilson, he favored compromising with Senator Henry Cabot Lodge and other "Reservationists."
The Cox–Roosevelt ticket was defeated by Republicans Warren G. Harding and Calvin Coolidge in the presidential election by a wide margin, and the Republican ticket carried every state outside of the South.
Roosevelt accepted the loss without issue and later reflected that the relationships and good will that he built in the 1920 campaign proved to be a major asset in his 1932 campaign.
The 1920 election also saw the first public participation of Eleanor Roosevelt who, with the support of Louis Howe, established herself as a valuable political ally.
Roosevelt's plan to convince Hoover to run for the Democratic nomination fell through after Hoover publicly declared himself to be a Republican, but Roosevelt nonetheless decided to seek the 1920 vice presidential nomination. After Governor James M. Cox of Ohio won the party's presidential nomination at the 1920 Democratic National Convention, he chose Roosevelt as his running mate, and the party formally nominated Roosevelt by acclamation. Although his nomination surprised most people, Roosevelt balanced the ticket as a moderate, a Wilsonian, and a prohibitionist with a famous name. Roosevelt had just turned 38, four years younger than Theodore had been when he received the same nomination from his party. Roosevelt resigned as Assistant Secretary of the Navy after the Democratic convention and campaigned across the nation for the Cox–Roosevelt ticket.
During the campaign, Cox and Roosevelt defended the Wilson administration and the League of Nations, both of which were unpopular in 1920. Roosevelt personally supported U.S. membership in the League of Nations, but, unlike Wilson, he favored compromising with Senator Henry Cabot Lodge and other "Reservationists." The Cox–Roosevelt ticket was defeated by Republicans Warren G. Harding and Calvin Coolidge in the presidential election by a wide margin, and the Republican ticket carried every state outside of the South. Roosevelt accepted the loss without issue and later reflected that the relationships and good will that he built in the 1920 campaign proved to be a major asset in his 1932 campaign. The 1920 election also saw the first public participation of Eleanor Roosevelt who, with the support of Louis Howe, established herself as a valuable political ally.
Franklin D. Roosevelt