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President-elect Donald Trump doesn't seem to have the support of his defense secretary nominee when it comes to scrapping the Iran nuclear deal on day one of his presidency. Retired Marine Gen. James Mattis said at his Senate confirmation hearing Thursday that while the deal is "an imperfect arms control agreement," he thinks the U.S. must uphold the deal — which Trump has dubbed "one of the dumbest deals ever."

Mattis argued the agreement, which involves the U.S. and five other countries lifting its sanctions on Iran in exchange for restrictions on its nuclear program, is integral to security in the region. "When America gives her word, we have to live up to it and work with our allies," Mattis said.

Watch Mattis diverge from Trump below. Becca Stanek