((John Hensdale - He has John C. Calhoun written all over him. Both of them held radical beliefs early on, Nullification for Calhoun and SNP for Hensdale, but near the end, displayed great lengths and huge calls to keep the Union together. Calhoun's time was in the 1850 Debates about the Compromise, with Hensdale teaming up with Brass to run for the Presidency.
Thomas L.J. Davis - Not much of a man, more of the personification and manifestation of the "Fire Eaters" at the time. Davis was remarkable in steering the emotions of the South towards sectionalism, which caused the creation of the SNP - and the very early split of National parties to Regional parties (In OTL it was time and all the Fire Eaters that did this, in TTL we have Davis.
Nicholas Khur - Although expanding into the Civil War, Khur reminds me most of William Tecumseh Sherman. Both born in the North, living in the South by the time war breaks out, they migrate North to engage in actives against the South in order to preserve the Union.
John F. Cameron - A hard one to place, for sure - but President Cameron holds his places as James K. Polk. Cameron and Polk, in a sense, both brought Texan Slavery to the United States. Both presidents also oversaw the Mexican-American war - and the Mexican cession along with it. Where Polk failed, Cameron succeeded by winning another term, generally keeping the nation pleased with themselves, and avoiding the big boiling pit that was the Slavery Debate.
Jeremiah Brass - Now this would be based widely on speculation of course, but I'd give Brass the benefit of being President Taylor. Staunchly against compromise and unwilling to allow concessions, Brass's mentality closely reflects what President Taylor would have done given the situation. Unfortunately for the SNM at the time, President Brass did not die randomly like Taylor did during the 1850 Compromise.
I'll update this as I get more time.))