Rivalry brewing on Trump team between Mattis and Flynn

But perhaps the biggest point of debate between Flynn and Mattis will be President-elect Donald Trump’s willingness to work more closely with Russia.

Mattis will head a department whose top military leaders — including Chairman of the Joint Chiefs of Staff Marine Gen. Joseph Dunford — have named Russia as the No. 1 threat to the U.S.

Mattis himself said May 2015 at The Heritage Foundation, “in the near term, I think the most dangerous might be Russia.”

Flynn, on the other hand, “doesn’t seem to have interest in that,” Barno said.

In the inevitable jockeying that occurs between top Cabinet officials, there’s reason to think Flynn could have the upper hand.

For one, experts note that Flynn will be in the White House and will have Trump’s ear everyday. Mattis, on the other hand, will likely see the president about once a week.