Sen. Lindsey Graham said Friday that the worst thing President-elect Donald Trump could do is “forgive and forget” what Russia did to interfere in the U.S. election.

“That screams weakness,” the South Carolina Republican and former rival of Mr. Trump said on “CBS This Morning” ahead of the inaugural ceremony in Washington, D.C.

In the first 100 days of the new administration, Graham said he plans to try to get a vote on a bipartisan bill to toughen sanctions against Russia to respond to its cyberattacks against the U.S. last year.

“There’s no doubt in my mind that Russia tried to undermine the election,” he said. “They didn’t change the outcome.”

Graham said he hopes that Mr. Trump will deliver an inaugural speech “that acknowledges that he’s a president of all of us,” even the protesters who are in town. He said that Rev. Jesse Jackson is encouraging him to work on an infrastructure bill with Mr. Trump and voiced confidence that Democrats would back that effort.

“Our bridges and roads are falling apart and we have to try to find a way to pay for it,” Graham said.

Asked if he’s optimistic as Mr. Trump takes office, Graham said, “Sure.” Then, he joked, “I don’t know if I’m on the kill list or not. That’d be good to know.”

Graham advised the president-elect to bring lawmakers and their families over to the White House to improve relations with Capitol Hill. He said he’s hopeful that Republicans can repeal and replace Obamacare and pass tax reform and regulatory reform.