Coming Up on This Week with George Stephanopoulos

— -- In a Sunday exclusive, George is joined by Sen. Barack Obama, D-Ill, following his victory in the pivotal South Carolina Democratic primary.

Obama reacts to his first-in-the-south win and weighs his chances in the Feb. 5th Super Tuesday races.

In the middle of one the most contentious primary races to date, hear what Obama has to say about his fiery battle with Democratic rival Sen. Hillary Clinton and what's next for his campaign. Has former Pres. Bill Clinton's campaigning gone too negative? Will hitting back change the Obama campaign's message of hope?

And on our Roundtable, Donna Brazile, Jacob Weisberg, Cokie Roberts, and George Will debate the week's politics.