Barack Obama says he's expecting "a split decision" in what almost shapes up as a national presidential primary Tuesday.

His Democratic rival Hillary Clinton wouldn't make a prediction during her round of morning TV show appearances, saying candidates are "all kind of guessing about what it's all going to mean because it's never happened before."

There are contests in 24 states. The stakes are huge: 1,023 Republican and 1,681 Democratic delegates. The number needed to win the nomination: 1,191 Republican and 2,025 Democratic.

West Virginia is the only state holding a GOP convention Tuesday, where Mitt Romney and Mike Huckabee each plan to make a personal appeal for the 18 delegates up for grabs.

Ron Paul also will attend the Charleston convention. Front-runner John McCain is sending former Louisiana Governor Buddy Roemer to speak on his behalf.