The director of the U.S. Cybersecurity and Infrastructure Security Agency said Tuesday's election saw "minor" disruptive activities, but the agency has seen "no evidence of malicious activity impacting the security or integrity of election infrastructure."

CISA director Jen Easterly told reporters that the hoax bomb threats that were sent to at least four states around the country were all deemed to be "non-credible."

"While disruptive, this was a threat that election officials prepared for and exercised for and effectively mitigated working closely with law enforcement partners," Easterly said.

Easterly urged vigilance "for continued attempts by our foreign adversaries to use false narratives and disinformation to undermine American confidence and the legitimacy of election."

Easterly also reiterated that she believes there was "no cheating" that occurred.

-ABC News' Luke Barr

Wisconsin's top election official said the decision to retabulate ballots in Milwaukee should preempt a potential future challenge to the election results in Wisconsin.

Officials decided to retabulate about 31,000 absentee ballots after a poll observer reported that a door to several tabulators was not properly sealed due to human error.

"Milwaukee made the decision to make sure this was addressed today, on Election Day in the public eye, so that no one could use a procedural misstep to call those legitimate votes into question later," said Wisconsin Election Commission Administrator Meagan Wolfe.

"We've got a lot of folks that would be able to vouch for the veracity of today's elections and that everything was administered in a fair and free way, and you're going to be able to get that information from firsthand accounts from individuals that were actually appointed to be there and fulfill those roles by the major parties," Wolfe said.

Wolfe confirmed ABC News' reporting that a non-credible Russian-based bomb threat had been made to a polling place in the city of Madison.

-ABC News' Peter Charalambous

Philadelphia city commissioner Seth Bluestein, a Republican, rebuked former President Donald Trump's claim earlier Tuesday that "cheating" took place in the city, emphasizing that the city worked closely with the Republican National Committee "in real time" to field complaints and that "there is no evidence whatsoever of massive cheating."

"If anybody has evidence of widespread cheating, please send it in, because we'd like to see it, and I guarantee you there won't be any," Bluestein said.

"Just think about everyone who stood up for democracy today," commission chair Omar Sabir, a Democrat, said -- his voice choked with emotion -- as he thanked election workers.

In Detroit, Michigan Secretary of State Jocelyn Benson called out Trump for sowing "seeds of doubt" about the election.

"If there are either candidates or other bad actors, or even foreign bad actors who try to continue to inject confusion or fear or sow seeds of doubt about the sanctity of their elections in the hours and days ahead, we'll be there to speak the truth and ensure people know what is actually happening," Benson said during a press conference at Detroit's Ford Field.

-ABC News' Christopher Boccia and Peter Charalambous

Milwaukee has called in reinforcements from other parts of the city government to help process ballots as it works through a backlog of 31,000 absentee ballots.

Approximately 40 city employees -- including firefighters, health employees, IT experts and librarians -- are assisting with the count of absentee ballots, according to a city official.

The absentee ballots are being retabulated after a door to several tabulators was not properly sealed due to human error, the Milwaukee mayor's office said.

As the counting continues, some Republicans have descended on the Baird Convention Center to ask about how this mistake happened.

"This seems like a real mess," Sen. Ron Johnson said.

Johnson said he showed up at the polling location to "ask questions" and "restore confidence" in the results. He said he believes the city was unprepared for the election.

Johnson was joined by GOP Chair Brian Schimming, who summed up the incident in a few words: "You had one job."

The Milwaukee Election Commission earlier said that the city "has no doubt regarding the integrity of the election."

"However, in order to eliminate any doubt to be fully transparent, the MEC has decided to start the tabulation process over for all ballots at Central Count. This decision was made in consultation with both Republican and Democratic officials," the commission said.