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With debate brewing over the Iran nuclear deal and the future of U.S. troops in Afghanistan, and new saber-rattling from China, George Stephanopoulos goes one-on-one with former Obama national security adviser Tom Donilon, only on "This Week."

And with Saturday's Nov. 30 deadline for a better-functioning HealthCare.gov website looming, the Affordable Care Act faces new obstacles, with a challenge to the Supreme Court over one of the law's provisions, and a year-long delay impacting small businesses using the federal health care website.

The powerhouse roundtable debates the major challenges at home and abroad, with Rep. Tom Cole, R-Okla., Rep. Keith Ellison, D-Minn., Wall Street Journal columnist Peggy Noonan, and former Obama White House Senior Adviser David Plouffe, now an ABC News and Bloomberg News contributor.

Plus, Americans gathered around the television screens this Thanksgiving for the latest NFL showdowns, with growing concerns over the impact of concussions on the game of football. Our special panel tackles that debate, with ABC News Chief Health and Medical Editor Dr. Richard Besser, USA Today columnist and ABC News consultant Christine Brennan, ESPN investigative reporter Mark Fainaru-Wada, co-author of "League of Denial: The NFL, Concussions and the Battle for Truth", and former Buffalo Bills offensive lineman and Pro Football Hall of Fame member Joe DeLamielleure.

And in our "Sunday Spotlight," U2 lead singer Bono, co-founder of ONE and the RED campaign, reflects on the progress battling HIV/AIDS on this Sunday's World AIDS Day.

See the whole political picture, Sunday on "This Week."

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