Worst Presidents: John Tyler (1841-1845)

He was a stalwart defender of slavery who abandoned his party's platform once he was president.

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Slideshow: Worst Presidents

At sixth worst, Virginian John Tyler was the first president to rise by succession from the vice presidency—when William Harrison succumbed to pneumonia only 30 days after being sworn into office.

Born into the planter aristocracy, Tyler began his political career as a Jefferson Republican, opposing Federalist schemes for high protective tariffs and federally funded "internal improvements."

As a U.S. senator, he supported President Andrew Jackson's crusade against the national bank but soon fell out with Old Hickory when he quashed South Carolina's attempt to nullify a modest tariff. (Tyler, a steady champion of states' rights and slavery, defended South Carolina's prerogative to secede if it wished.)

Joining the young Whig Party, he ran with popular war hero Harrison, and the ticket of "Tippecanoe and Tyler Too" trounced the Democratic candidates.

But once he became president, Tyler opposed everything his adopted party stood for, including a national bank. One fellow Whig accused Tyler of reviving "the condemned and repudiated doctrines and practices of the worst days of Jackson's rule." The entire Harrison-appointed cabinet resigned, and Tyler had to fight an attempt to impeach him.

His one triumph: establishing the principle that a vice president who succeeds to the top office has no less authority than an elected president. No small accomplishment when most of his own party despised him.