Picking a running mate is the most important first decision of the presumptive (McCain) and potential (Clinton and Obama) nominees for president.
Though the first three Vice Presidents to ascend to the White House (Tyler, Fillmore, and Johnson) were a rum lot, we might have done worse. Richard Johnson of Tennessee (Van Buren’s number two) maintained one of his slaves as his common-law wife, while Schuyler Colfax (Grant’s first vice president) was up to his elbows in payola from the railroads. Since 1880, though, the vice presidential picture has (mostly) improved.
Chester Arthur of New York became president after James Garfield’s assassination in 1881. Though never elected to any public office in his own right, Arthur was quite able.
Unlike the four vice presidents who became president in the nineteenth century, all four who inherited the White House in the twentieth century each went on to win his own term.
Theodore Roosevelt of New York, succeeding William McKinley after his 1901 assassination, ended up dwarfing the man who led their ticket in the presidential campaign the year before. Calvin Coolidge of Massachusetts was a distinct improvement over Warren Harding, who died in office in 1923.

Coolidge
Harry Truman of Missouri entered the White House in 1945 after the death of Franklin Roosevelt died in 1945, while Lyndon Johnson of Texas succeeded John Kennedy in 1963. Both proved capable chief executives; both declined to seek an second elected term because he had led the nation into an unpopular Asian war.
Of our last three vice presidents, two fall into a category that might be called the “monarch butterfly defense.” An inoffensive creature without weapons against predators, the butterfly’s survival has been connected to a simple fact: it tastes terrible. Predators learn to leave it alone.
By choosing Dan Quayle and Dick Cheney as their vice presidents, the Presidents Bush have adapted the butterfly’s defense. You can kill or impeach me, the message goes, but it’s going to taste terrible: look what you’ll end up with! A version of this reasoning arose 140 years ago.
Union General (and political manipulator par excellence) Ben Butler of Massachusetts claimed that Lincoln had offered him the vice presidency in 1864. This story of Butler’s, known as “Beast Butler” to Southerners due to his command of occupying troops in New Orleans, is not credited by some historians of the era. He claimed that he refused to accept the position unless Lincoln could guarantee that he would die in office and leave Butler as President.

Butler
After Lincoln’s assassination, Butler brayed that it was a shame he had not accepted the vice presidency. John Wilkes Booth would never have assassinated Lincoln, Butler insisted, if he thought Butler would become president!