As a response to the Russian campaign to sow discord in the 2016 presidential election, the so-called Honest Ads Act is wholly inadequate. It is also entirely necessary.

The legislation, introduced last week by Democratic senators Mark Warner of Virginia and Amy Klobuchar of Minnesota, requires online platforms with at least 50 million monthly users -- think Facebook, Google and Twitter -- to make a public record of advertisers who spend at least $500 on political ads regarding campaigns or significant legislative issues. The record would include information regarding the ad's content, its target audience and its cumulative views, as well as its cost. It would also list any candidate referred to in the ad and contact information for the entity that purchased it.

All this information would be placed in a publicly accessible database. Under the legislation, platforms would be required to make "reasonable efforts" to police foreign purchases.

True, this legislation focuses solely on advertising, so would not have prevented some of the most successful subversions of the 2016 election -- the Russian propaganda that spread over social networks as unpaid media. Still, a U.S. defense against election interference has to begin somewhere. Russians spent at least $100,000 on Facebook ads. Warner, the ranking Democrat on the Senate Intelligence Committee, has said he believes such spending constitutes the "tip of the iceberg."

The challenge will only grow more complex as the internet becomes an ever-larger conduit for political communication. Digital spending reached $1.4 billion in the 2016 election, up more than 700 percent over 2012.

Representatives from Facebook, Google and Twitter will testify before House and Senate panels next week. They should come prepared with suggestions on how their powerful, pervasive and lucrative platforms can help root out foreign agents seeking to undermine American democracy, through paid advertising and otherwise. It's not an impossible task: Internet platforms shut down thousands of suspicious accounts during last spring's French election.

Requiring online platforms to perform the minimal record-keeping and due diligence required of television and radio stations is a necessary step toward protecting the integrity of U.S. elections. This is a cause that transcends both commercial and partisan concerns -- the bill has the support of Republican Senator John McCain. Congress should pass the Honest Ads Act. Then build on it.