The group that approached Clinton's aides, led by Halderman and voting-rights attorney John Bonifaz, contacted the campaign this week. That call, which was first reported by New York Magazine, raised the possibility that Clinton may have received fewer votes than expected in some counties that rely on electronic voting machines.
But Halderman stressed in his Medium post that the group has no evidence of a cyberattack or voting irregularities. He urged that a recount be ordered just to eliminate the possibility.
"The only way to know whether a cyberattack changed the result is to closely examine the available physical evidence -- paper ballots and voting equipment in critical states like Wisconsin, Michigan and Pennsylvania," Halderman wrote.
Wednesday afternoon, Green Party presidential candidate Jill Stein announced an effort to raise $2.5 million by Friday afternoon to pay for recounts in the three states. The campaign appeared to have raised nearly $800,000 in its first several hours.
According to results from the three states, President-elect Donald Trump won Pennsylvania by about 70,000 votes of more than 6 million ballots cast, for a 1.2 percent edge over Clinton. He is shown winning Wisconsin by 22,000 votes of nearly 3 million votes cast, or .8 percent; and Michigan by just over 10,000 votes out of 4.8 million, or .2 percent. All three states had voted Democratic in recent presidential elections.
An AP request to the Trump transition team for comment was not immediately returned.
Trump's campaign had long believed that his message of economic populism would resonate in the Rust Belt. He frequently campaigned in Pennsylvania and made a late push in both Wisconsin and Michigan, successfully turning out white working-class voters whom pollsters may have missed.
Many pre-election polls showed Clinton with slight leads. While advocating for the recounts, Halderman writes that "the most likely explanation" for Trump's surprise win "is that the polls were systematically wrong,"
The deadlines for petitioning for a recount in all three states are in the coming days, with Wisconsin's on Friday.
The focal point of any possible electoral cyberattack presumably would have been electronic voting machines that, whether or not they are connected to the internet, could be infected with malware that could change vote totals. But many of those machines produce a paper record of the vote that could be checked to see if the vote tabulations are accurate.
Pennsylvania is considered one of the states most susceptible to hacking because 96 percent of its voting machines have no paper trail. Wisconsin is far less vulnerable because it uses electronic machines with voter-verifiable paper trails in most counties. Michigan is considered the safest of the three because it uses paper ballots.
Many election experts have called for routine post-election audits designed to boost public confidence in vote outcomes, by guarding against both tampering and natural vote-counting mistakes. These could involve spot checks of the voting records and ballots, typically in randomly selected precincts, to make sure that votes were accurately recorded.
In many states, audits involve hand-counting the votes on paper ballots and comparing the results to the totals stored in the state's electronic voting system. Such audits do sometimes turn up mistakes that reverse an election. That happened in Florida's Palm Beach County in 2012, when a post-election audit determined that the "winners" in two city council races were actually losers.
Routine audits also make it possible to confirm the accuracy of elections without putting the onus on losing candidates to call for a recount. In states without regular audits, a candidate who questions the results gets "painted as a sore loser," Pamela Smith, president of the nonprofit Verified Voting, said in an interview earlier this year. "If you do a regular audit, you often don't need a recount. It either shows the count was right or you find something."
Any attempted hack to swing the results in three states would have been a massive and unprecedented undertaking. But electoral security was an issue that loomed large in many Americans minds this year as the Democratic National Committee and several Clinton staffers had their emails breached and later released. U.S. security officials believe that hack of email was orchestrated by Russian hackers.
