EXCLUSIVE: Tim Matheson Explains Why 'Killing Reagan' Is Different Than Bill O'Reilly's Other TV Adaptations

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Tim Matheson is the spitting image of Ronald Reagan in the TV movie, Killing Reagan, and he stayed in character when ET's Nischelle Turner spoke with him on the set.

The project is National Geographic Channel's third adaptation of Bill O'Reilly and Martin Dugard's "Killing" book series, following Killing Lincoln and Killing Kennedy. Matheson explained what sets this story apart from the others.

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"It really is a biopic of he and Nancy and his presidency and [John Hinckley, Jr.], all these converging things, which the other stories -- Killing Lincoln and Killing Kennedy -- didn't have," Matheson said.

The 40th President of the United States served two terms in office, from 1981 to 1989. Just 69 days after taking office, Reagan was shot by John Hinckley, Jr., the then 25-year-old son of a wealthy oil executive. Hinckley, Jr. stepped out of a crowd outside the Hilton Hotel in Washington, D.C., and opened fire with a six-shot revolver as the president left a speaking engagement.

After a quick recovery, Reagan returned to duty, attempting to restore prosperity to the country. During his second term, he would promote a message of achieving "peace through strength" abroad, and negotiated a treaty with Soviet leader Mikhail Gorbachev that would eliminate intermediate-range nuclear missiles. In 1984, Reagan told Time magazine that he dreamed of one day eliminating all nuclear weapons.

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During the ups and downs of Reagan's political career, there were many changes, but one thing remained the same, his wife Nancy's undying love for him. Despite disagreeing with Nancy's politics in real life, actress Cynthia Nixon, who portrays the former first lady in the TV movie, focused on Nancy's loyalty to her husband for her performance.

"If you have to boil Nancy Reagan down to one single quality it was that she was crazy in love with her husband," Nixon said, "and Tim Matheson is a very easy person to love, so most of my work was done before I arrived."

Killing Reagan premieres Sunday at 8 p.m. PT/ET on the National Geographic Channel.