Franklin D. Roosevelt won elections for his first two presidential terms in landslides and went on to become the only U.S. president to win a third and fourth term. However, the Democratic president’s popularity was not universal—not within his party or even on his own presidential ticket. His first vice president, John Nance Garner III, was so fiercely opposed to FDR’s policies and his idea of running for an unprecedented third term that Garner entered the 1940 race to be Democratic nominee for president.

Though Garner had many supporters in the more conservative wing of the Democratic party, FDR was able to outmaneuver him, arranging for his own “spontaneous” nomination at the 1940 Democratic National Convention. FDR dumped Garner for a new running mate at the convention, and for the rest of FDR and Garner’s term together, the relationship between the two men remained decidedly cool.

Like many vice presidential candidates, Garner was one of the candidates in his party’s presidential primary the year that FDR tapped him to be his running mate. FDR’s first election took place in 1932, a period in which the Democratic Party’s base included both white conservatives in the south and Catholics and immigrants in the north and west. This was an awkward coalition, and tapping Garner—a conservative Democrat from Texas—helped FDR—who was then governor of New York—shore up support within his party.

Roosevelt and Garner won the 1932 election in a landslide, unseating incumbent president Herbert Hoover, who only carried six states. FDR immediately went to work designing legislation to address the Great Depression; and in so doing, took on a larger role in crafting legislation than any president before him. Garner, who’d served in the U.S. House of Representatives for 30 years and had briefly been its Speaker, used his relationships with members of Congress to lobby in favor of this legislation. At least, for the first few years.

Garner was an anti-labor conservative who opposed the amount of federal spending in the New Deal. By 1935, Garner grew increasingly unhappy with the legislation he was supposed to promote, as FDR pushed forward the Wagner Act, which established the right of workers to join unions​​; the Revenue Act, which introduced a wealth tax; and the Social Security Act—all of which Garner personally opposed.

In 1936, FDR and Garner won a second term in the largest political landslide since the modern development of the Republican and Democratic Parties. Alf Landon, the Republican challenger, carried only two states and received eight electoral votes. However, after this victory, FDR made a series of decisions that weakened him politically.

Roosevelt’s attempt to balance the federal budget helped cause a short-term recession, and his decision not to consult with many people before revealing his 1937 “court packing” plan eroded some of his popularity. With the president’s popularity dwindling, Garner made little effort to hide his contempt for the Supreme Court plan among members of Congress, writes Robert A. Caro in The Years of Lyndon Johnson: The Path to Power, and the plan ultimately failed.

READ MORE: How FDR Served Four Terms as U.S. President

During FDR’s dip in popularity, “Garner probably felt a little more free to be critical of Roosevelt and the Supreme Court packing plan, but he wasn’t alone,” says David B. Woolner, a history professor at Marist College and senior fellow at the Roosevelt Institute.

“We tend to forget that Roosevelt’s biggest enemies in many respects were not Republicans but Democrats,” he says. “The conservative southern Democrats were really hostile to Roosevelt’s New Deal, and Garner represents that same wing of the Democratic party.”

Garner’s biggest break from FDR occurred during the 1938 midterms, when FDR conducted what Garner considered a “purge” of the more conservative Democrats in Congress by backing more liberal candidates in Democratic primaries. Garner viewed these conservative Democrats as colleagues and friends, and he was angry that FDR was backing more liberal candidates.

Upset by growing speculation that Roosevelt might run for a third term, Garner ended up entering the Democratic primaries in late 1939. According to a Gallop Poll that March, 45 percent of respondents said that they’d like to see Garner elected president if Roosevelt didn’t run; and 53 percent of Democratic respondents said that they opposed FDR running for a third term.

But despite opposition from the conservative wing of the party, Roosevelt remained a powerful, and generally still pretty popular, president. The outbreak of war in Europe in 1939, and the war’s worsening in 1940, may have also made keeping the current president seem like a safer bet.

In any case, Roosevelt ended up beating Garner without even running in the primaries (which were still a new development and not yet as important as they would be later on in determining a candidate). At the 1940 Democratic National Convention, where FDR arranged for his own nomination, the sitting president received 946 of the delegate votes, while Garner received 61.

Instead of choosing the vice president who had become openly hostile to his agenda, FDR chose the much more liberal Henry A. Wallace as his running mate. FDR and Garner finished their term together, but after Garner left the White House, Woolner says, “I’m not even sure that the two men ever spoke again.”