The letter, signed on Monday, centers around a batch of documents released by the New York Post last week that purport to tie the Democratic nominee to his son Hunter’s business dealings. Under the banner headline “Biden Secret E-mails,” the Post reported it was given a copy of Hunter Biden’s laptop hard drive by President Donald Trump’s personal lawyer Rudy Giuliani, who said he got it from a Mac shop owner in Delaware who also alerted the FBI.

While the letter’s signatories presented no new evidence, they said their national security experience had made them “deeply suspicious that the Russian government played a significant role in this case” and cited several elements of the story that suggested the Kremlin’s hand at work.

“If we are right,” they added, “this is Russia trying to influence how Americans vote in this election, and we believe strongly that Americans need to be aware of this.”