WASHINGTON (CBSNewYork) — President Donald Trump fired off tweets Sunday saying the Obama administration was to blame for Russian meddling in the 2016 election.

Meanwhile, as CBS News’ Laura Podesta reported, lawmakers on both sides of the aisle said something must be done to stop future interference.

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Trump pointed fingers at the Obama administration for not stopping Russian operatives from interfering in the 2016 election.

Trump also defended his victory, saying the results of the 2016 election were not affected by any meddling.

“It’s hard to say that this didn’t affect the outcome,” said U.S. Sen. Chris Coons (D-Delaware). “It was an exceptionally close election. I’ll remind you one candidate won the popular vote. The other candidate won the electoral vote. But it’s not yet clear whether the Russians succeeded in actually changing votes.”

The Department of Justice has indicted 13 Russians and three Russian companies for creating hundreds of fake social media profiles. They posted attacks on Clinton, while praising Democratic primary rival Sen. Bernie Sanders (I-Vermont) and then-candidate Trump.

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On Sunday morning political shows, Democrats and Republicans agreed the U.S. needs to continue to tighten its security against Russian infiltration, especially before the midterm elections.

“The Department of Homeland Security has been very aggressive working with states under this administration to be able to work on election security,” said U.S. Sen. James Lankford (R-Oklahoma).

To stop Russians from purchasing political ads, Facebook now says it will require potential advertisers to have a U.S. address. The company will send postcards with a code to complete the transaction.

The hope is that only people who reside in the U.S. will be able to influence future U.S. elections.

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The latest indictment did not accuse anyone from the Trump campaign of coordinating or working with Russians. Special Counsel Robert Mueller’s broader investigation is ongoing.