Republican Sen. Rob Portman is urging President Trump to "explicitly" tell his supporters to "remain peaceful and refrain from violence" in the runup to President-elect Joe Biden's inauguration as lawmakers grow increasingly concerned about the potential for another riot like the one at the Capitol last week. 

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"If our nation experiences additional violence and destruction at the hands of his supporters in Washington, D.C., and state capitols around the country, and he does not directly and unambiguously speak out now when threats are known, he will bear responsibility," Portman, R.-Ohio, said in a statement Tuesday. 

Portman made the statement a week after a Trump rally on Jan. 6 where the president urged his supporters to "fight" for the "stolen election" after which a mob of them stormed the Capitol, forcing lawmakers into hiding. 

"Both in his words before the attack on the Capitol and in his actions afterward," Trump "bears some responsibility for what happens," Portman said.

Five people, including a U.S. Capitol Police officer, died in the unprecedented attack.

Trump on Tuesday defended his language and his response to the attacks, calling it "totally appropriate."

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Despite heightened alarm about further violence, President-elect Joe Biden has said he intends to carry on as planned with the inauguration, which will take place Jan. 20 outside the Capitol building. The event's theme is "America United."

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Officials increased the number of National Guard members deployed in Washington during the presidential inauguration from 15,000 to 20,000 on Wednesday, about three times the number of U.S. troops currently deployed to Iraq and Afghanistan combined.