ATLANTA — The collusion question now answered, another one looms ahead of 2020: Will U.S. elections be secure from more Russian interference?

The 22-month-long special counsel investigation underscored how vulnerable the U.S. was to a foreign adversary seeking to sow discord on social media, spread misinformation and exploit security gaps in state election systems.

With the presidential primaries less than a year away, security experts and elected officials wonder whether the federal government and the states have done enough since 2016 to fend off another attack by Russia or other hostile foreign actors.

“Although we believe that Russia didn’t succeed in changing any vote totals, the Russian playbook is out there for other adversaries to use,” said Virginia Sen. Mark Warner, a Democrat and vice chairman of the Senate Committee on Intelligence. “As we head towards the 2020 presidential elections, we’ve got to be more proactive in protecting our democratic process.”

Special counsel Robert Mueller detailed the sweeping conspiracy by the Kremlin to meddle in the 2016 election in an indictment last year, charging 12 Russian military intelligence officers with hacking the email accounts of Clinton campaign officials and breaching the networks of the Democratic Party. The indictment also included allegations the Russians conspired to hack state election systems and stole information on about 500,000 voters from one state board of elections’computers.

Another indictment from the special counsel detailed Russia’s use of social media and fake accounts to spread divisive rhetoric and undermine the U.S. political system.

Since the 2016 race, Facebook, Google and other internet giants have thrown millions of dollars, tens of thousands of people and what they say are their best technical efforts to identify misinformation, illegal political manipulation and hate that proliferate on their digital platforms.

Federal, state and local election officials have scrambled to improve communications and coordination, increase cybersecurity and upgrade outdated voting equipment. Congress last year sent $380 million in grants to states to help pay for some of these upgrades, but cybersecurity experts say that was just a down payment and much more is needed.

Although there was no evidence of large-scale interference in 2018, security experts and even government officials have acknowledged the likelihood that foreign adversaries stayed on the sidelines in preparation for next year’s presidential election.

U.S. intelligence officials have said Russia, China, Iran and other countries remain interested in influencing U.S. policy, and elections are a top target.

“We’re much better prepared in that we’re aware that there is a threat,” said Lawrence Norden, an expert on voting machines with the Brennan Center for Justice at New York University’s law school. “But we haven’t done some basic things.”