An election security expert told Congress that the biggest challenge going into November's election is not vote security but the public's confidence in the system.

John Gilligan, president and CEO of the Center for Internet Security – an organization that provides election security advice – said Tuesday that when it comes to faith in the voting process, the last presidential election was as bad as it gets.

TRUMP ENCOURAGES FLORIDA TO VOTE BY MAIL, CALLS SYSTEM 'SAFE AND SECURE'

"I actually think to some extent we saw the worst-case scenario in 2016," Gilligan told the House Homeland Security subcommittee on Cybersecurity, Infrastructure Protection & Innovation. "And let me explain what I mean by that. I think the actual vote capturer tally systems, which is where the actual vote is captured and then it is counted, those systems tend to be highly resilient and they're not easily accessible. You almost have to get physical access to them which makes the threat, execute the threat fairly difficult."

Gilligan explained that the vulnerabilities are in the "many other elements of the elections infrastructure" that are connected to a network. He said that after the 2016 election, he spoke to officials who were satisfied that no votes were altered, but that this missed the whole picture.

"But as we all know, it wasn't just that the vote was cast and counted properly, it's what's the confidence level the American public has in the system," he said. "And therefore an attack against the voter registration system, which did not result in anyone not being able to vote, or any changes to votes, became a symbol to our American public that there's something going on here, and therefore I'm losing confidence."

TRUMP CAMPAIGN REFOCUSES FIREPOWER ON EARLY VOTING, WITH JUST WEEKS TO GO UNTIL START

Looking ahead to November's election, Gilligan said the same problem regarding confidence in the system is present, and that the public must be kept informed in order to trust that the system is indeed secure.

"I believe the biggest challenge we continue to have into 2020," Gilligan said, "is to be able to ensure that the American public has clear information about what is being done to protect the systems, and if there is any particular event to be able to very clearly identify what’s the impact and there had been lots of procedures put in place and if there is a small glitch that will not impact the counting of the vote or the ability to cast the vote."

Sylvia Albert, director of voting and elections for nonprofit group Common Cause, testified at the hearing that President Trump's comments about election security have swayed public perception.

"We have seen already that the president's rhetoric is affecting the confidence that voters have both in vote-by-mail particularly and also in elections in general," Albert said.

CLICK HERE TO GET THE FOX NEWS APP

The president's warnings about vote security have focused on mail-in voting. Republicans have voiced concerns that voting by mail on a large scale exposes the system to fraud. However, election officials and other election experts have said that mail-in voting is secure and that states protocols to protect against fraud.

On Tuesday, Trump expressed confidence that at least the state of Florida – where he has voted via absentee ballot in the past – has a safe and secure system, and encouraged voters to vote by mail there.