"If she wins Texas and Ohio, I think she will be the nominee. If you don't deliver for her, I don't think she can be. It's all on you," former President Bill Clinton declared in the lead up to the vote in those states.
And, once again, with her campaign on the line, Clinton pulled out a significant victory, winning both the Texas and Ohio primaries and vowing to fight on to the next biggest contest in Pennsylvania.
Obama picked up expected wins in Wyoming and Mississippi, sending the race into its longest lull since voting began -- six weeks between the contest March 11 in Mississippi and the next vote in Pennsylvania April 22.
In that time, Obama faced undoubtedly the toughest test of his campaign.
Controversy erupted around the Rev. Jeremiah Wright, Obama's pastor at Trinity United Church of Christ for more than 20 years, when ABC News' "Good Morning America" aired sermons in which Wright repeatedly denounced the United States based on what he described as his reading of the Gospels and the treatment of black Americans.
"The government gives them the drugs, builds bigger prisons, passes a three-strike law and then wants us to sing 'God Bless America.' No, no, no, God damn America, that's in the Bible for killing innocent people," he said in a 2003 sermon. "God damn America for treating our citizens as less than human. God damn America for as long as she acts like she is God and she is supreme."
Wright also told his congregation on the Sunday after Sept. 11, 2001, that the United States had brought on al Qaeda's attacks because of its own terrorism and claimed the U.S. government might have created the AIDS virus to harm blacks.
Obama initially defended Wright in a widely lauded speech on race.
"He strengthened my faith, officiated at my wedding and baptized my children," Obama said in that speech. "I can no more disown him than I can disown the black community. I can no more disown him than I can my white grandmother -- a woman who helped raise me, a woman who sacrificed again and again for me, a woman who loves me as much as she loves anything in this world, but a woman who once confessed her fear of black men who passed by her on the street, and who, on more than one occasion, has uttered racial or ethnic stereotypes that made me cringe."
But several weeks later, when Wright reappeared and affirmed many of the controversial statements he had previously made, Obama cut ties with the reverend and denounced him.
"The person I saw yesterday was not the person I met 20 years ago," the Illinois senator said at a press conference in Winston-Salem, N.C. "His comments were not only divisive and destructive, but they end up giving comfort to those that prey on hate."
For her part, Clinton largely resisted commenting on the controversy, although she did call Wright's remarks "offensive and outrageous."
But, privately, many Clinton aides admitted they were hearing from superdelegates concerned about Wright's controversial remarks.
During that same time, Clinton also faced controversy surrounding an exaggerated description she gave of a 1996 trip to Bosnia.
Clinton said she and her crew landed in an "evasive maneuver under sniper fire," describing her trip to Tuzla as if it were a scene from "Saving Private Ryan."
"There was supposed to be some sort of greeting ceremony, but instead we just ran with our heads down to get into the vehicles," she said.