WASHINGTON — Sen. Bill Nelson (D-Fla.) is standing by his claims that Russian hackers have already penetrated some of Florida’s voting registration systems ahead of the midterm elections, despite swift backlash from Gov. Rick Scott, who is challenging the senator in this year’s election.

• Sen. Nelson stands by Russian hacker claims, amid pushback
• Expert: perception of possible hackers could have impact on voters
• Threat of interference at all-time high, says cybersecurity expert

While both the Department of Homeland Security and the Florida Secretary of State say they have seen no new compromise from Russian actors, Senate Intelligence Committee members have declined to confirm or deny Nelson’s statements.

"It's unfortunate that some Florida officials have made this into a partisan political issue," Sen. Nelson said on Wednesday in Washington.

"Sen. Rubio and I reached out to Florida elections officials in each of the counties at the request of the leadership of the Senate Intelligence Committee to warn them about what the Russians are continuing from being in Florida in 2016," he explained.

"That warning has been out there since July 2, the letter that Senator Rubio and I sent," Sen. Nelson said.

“It’s really important that officials who are talking about these issues find a way to raise the concerns about the vulnerabilities without undermining people’s confidence in the election system themselves," said Laura Rosenberger, the director of the Alliance for Securing Democracy, which monitors interference in elections.

Sen. Nelson’s claims have not been denied or verified by the Senate Intelligence Committee. But Rosenberger, a former Clinton campaign foreign policy advisor, says his comments play into a larger problem.

“Without the kind of clear information, clear mechanisms of communication and real transparency on the part of government, that’s leading to messaging that people find very confusing," Rosenberger said

According to Rosenberger, even if hackers aren't intruding into election infrastructure, the perception can have an impact.

"An adversary doesn’t actually need to get in there and change votes in order to instill doubt and chaos in people’s minds," she said.

Attempts by Russian actors to penetrate Florida’s election system during the 2016 presidential election have been widely reported, most recently documented in Special Counsel Robert Mueller’s indictment of 12 Russian intelligence officers last month.

Cybersecurity experts say they could be trying again.

“It’s absolutely entirely plausible that there’s already could have been data theft to some extent," said Ron Bushar, the government chief technology officer for FireEye, a cybersecurity firm that has been tracking Russian hacker groups.

Bushar says it can take months to uncover these attempts from foreign actors and attribution can be difficult.

“Being able to say that this compromise of somebody’s email was definitely these Russian groups, or it was a state sponsored entity. That’s not something we arrive at overnight," Bushar said.

With the midterm elections just months away, Bushar says the threat of interference is at an all-time high, adding new urgency to concerns about hacking.

"This could potentially be strategically seen as a trial period in the run up to the next presidential cycle," he added.