General Discussion

but I could not recall the specific case... thanks.

As I recall Franklin Pierce was a 'dark-horse nominee', perhaps the 'classic' dark horse presidential nominee, who had no notable record on issues regarding slavery--- thus he became the nominee of the Democratic party of that time, who were on the verge of splitting between north and south over the slavery issue, but the Pierce nomination allowed them to be "all things to all people" in the 1852 election...

After his election, he clearly sided with southern Democrats over slavery and supported "Kansas-Nebraska" act, which split the party regionally about Pierce, and thus prevented his renomination in 1856.

So in 1856, the Democrats opted for Buchanan, who luckily for himself had spent many of the most recent years serving as an ambassador outside of the country, and thus had not been making any political arguments about slavery one way or the other...
(Echoes of the 1852 Pierce nomination).

Of course Buchanan, probably the most experienced and "most qualified EVER" presidential nominee offered by the Democratic Party--- his major claim to fame was presiding over the dissolution of the country and the secession from the Union of the various southern states just prior to the civil war. He said that it was illegal--- but also said that he could do nothing about it.