On July 31, 1844, Rhett launched the
Bluffton Movement, which called for South Carolina to return to nullification or else declare secession. It was soon repudiated by more moderate South Carolina Democrats, including even Senator
John C. Calhoun, who feared it would endanger the presidential candidacy of
James K. Polk. Rhett opposed the
Compromise of 1850 as against the interests of the slave-holding South. He joined fellow Fire-Eaters at the
Nashville Convention of 1850, which failed to endorse his aim of secession for the whole South. After the Nashville Convention, Rhett,
William Lowndes Yancey, and a few others met in
Macon,
Georgia on August 21, 1850, and formed the short-lived Southern National Party. In December 1850, he was elected by the South Carolina Legislature to be a U.S. Senator to complete the term left by the death of Calhoun. Rhett was the second to be elected to serve the remainder of Calhoun's term. The South Carolina Legislature initially elected
Franklin Elmore, but Elmore died shortly after taking office, and long before the conclusion of Calhoun's term. Rhett continued to advocate secession in response to the Compromise, but in 1852, South Carolina refrained from declaring secession and merely passed an ordinance declaring a state's right to secede. Disappointed, he resigned his Senate seat. He continued to express his fiery secessionist sentiments through the
Charleston Mercury, now edited by his son,
Robert Barnwell Rhett Jr. The
1860 Democratic National Convention met in
Charleston,
South Carolina and a large bloc of Southern delegates walked out when the platform was insufficiently pro-slavery. That led to the division of the party and separate Northern and Southern nominees for president, which practically guaranteed the election of an anti-slavery
Republican, which in turn triggered declarations of secession in seven states. During the
1860 presidential campaign, a widely credited report in the
Nashville Patriot said that the outcome was the intended result of a conspiracy by Rhett, Yancey, and
William Porcher Miles hatched at the Southern Convention in
Montgomery, Alabama in May 1858. One 20th-century historian called the scheme the work of "Rhett–Yancey–
Keitt extremists." ==Confederate States==