FACTBOX - Hillary Clinton's last stand in Ohio and Texas

(Reuters) - Democrat Hillary Clinton faces two crucial and potentially "must-win" showdowns with presidential rival Barack Obama in Ohio and Texas on Tuesday.

Here are some views on Clinton's challenges and her options if she fails to win both states with big enough margins to cut into Obama's current lead in pledged delegates, who will choose the Democratic nominee in November's election.

BARACK OBAMA, Illinois senator and candidate, in ABC interview.

"If we do well in Texas and Ohio, I think the math is such where it's going to be hard for her to win the nomination. And they'll have to make a decision about how much longer they want to pursue it."

CAL JILLSON, a political scientist at Southern Methodist University in Dallas.

"There will be people in her campaign who will argue a split decision is good enough to continue. But as a practical matter, just looking at the delegates, the numbers won't really add up for her."

BILL RICHARDSON, governor of New Mexico who dropped his presidential bid in January, on CBS' "Face the Nation."

"We have to have a positive campaign after Tuesday. Whoever has the most delegates after Tuesday, a clear lead, should be, in my judgment, the nominee."

MARK PENN, Clinton strategist.