At the event, Nielsen said the cyberthreat that now exceeds the danger of a physical attack against the U.S. by a hostile foreign group.
Wray told reporters that compared to 2016, in 2018, "We are not yet seeing the same kind of efforts to specifically target election infrastructure," but that other efforts to influence public opinion continue.
On Capitol Hill, lawmakers in both parties have pushed election security toward the top of the coming fall agenda amid heightened concerns about interference by Russians and others ahead of the midterm elections.
Asked this week how confident he was in the integrity of election systems ahead of the fall midterms, the No. 2 Republican, Sen. John Cornyn of Texas, said, "I'm confident we're doing the best we can."
Beyond Russian interference with social media campaigns to influence voters, lawmakers are increasingly looking at how to bolster election infrastructure in the states - even though Congress shot down a recent effort to boost federal funding for local and state systems.
Both Republicans and Democrats have criticized the administration's response as fragmented, without enough coordination across federal agencies. And with the midterms just three months away, critics are calling on Trump to take a stronger stand on an issue critical to American democracy.
The Senate is working on a bipartisan package backed by GOP leaders that would boost federal assistance to state and local election officials with cybersecurity guidelines, data sharing and security clearances. It's expected in September. GOP lawmakers are wary of being seen as imposing any new regulations on states that have resisted federal control.
Bolton said Trump is "leading unprecedented action to punish Russia" for its efforts to disrupt American elections.
AP writer Colleen Long, Lisa Mascaro and Deb Riechmann contributed.