After months of congressional investigations into Russian interference with U.S. elections, legislation is gaining traction as senators introduced a bipartisan plan to impose new disclosure requirements for political ads on Facebook, Twitter, Google and other social media.

"Election security is national security," said Democratic Sen. Amy Klobuchar at a news conference Thursday announcing a bill to require disclosure of who is paying for online political ads. Internet social networks are "dwarfing" broadcasters in the number of users, she said, adding, "Americans deserve to know who is paying for the online ads."

GOP Sen. John McCain gave a big boost to the proposal by Klobuchar and Democrat Mark Warner, announcing he will co-sponsor the bill.