WASHINGTON — The Hillary Clinton campaign Monday escalated its efforts to discredit FBI Director James Comey’s disclosure of a revived e-mail investigation, accusing him of applying a double standard for refusing to publicly discuss investigations of Russian meddling in the presidential election.

Comey has come under intense fire for his unusual disclosure to Congress Friday about the discovery of e-mails that the FBI planned to review, a statement that departed from Department of Justice policies to avoid investigative pronouncements shortly before elections.

The Department of Justice sent a letter to Congress Monday saying it would work with the FBI to “expeditiously’’ conduct a review. But it was uncertain that the law enforcement officials would conclude the revived probe of thousands of e-mails before the Nov. 8 election, and the cloud of innuendo created by Comey appeared likely to hang over Clinton’s bid throughout the final week of the campaign.

With polls showing a tightening race amid a damaging controversy, Clinton and her campaign officials rolled out fresh tactics Monday.

‘‘There is no case here,’’ Clinton said of the FBI review Monday, while campaigning in Ohio at Kent State University. She said the FBI “jumped into an election with no evidence of any wrongdoing.’’

Donald Trump continued to focus his attacks on the new FBI development as he stumped in Michigan, a state that polls — not to mention history — suggest is out of reach for him to win. The last time a Republican presidential candidate won Michigan was 1988.

‘‘Her election would mire our government and our country in a constitutional crisis that we cannot afford,’’ Trump declared in Grand Rapids. He said that the revived inquiry meant Clinton, if elected, could face a criminal trial as president.

Clinton’s campaign officials sought to turn the tables more aggressively on Comey, seizing on a report by CNBC. The cable TV channel cited an anonymous source Monday contending that sometime before Oct. 7 Comey had privately argued against US government agencies’ publicly fingering Russia for hacking efforts aimed at meddling in the election. Comey had reportedly argued that it was too close to Election Day to raise the accusation.

“It’s impossible to view this as anything less than a blatant double standard,’’ Clinton campaign manager Robby Mook told reporters on a conference call Monday. “That Director Comey would show more discretion in a matter concerning a foreign state actor than one involving the Democratic nominee for president is nothing short of jaw dropping.’’

The CNBC report “suggests that Comey feels compelled to make disclosures about e-mails that he’s not even read and admits may not be significant, but is insisting on discretion about Russian cyber attacks,’’ said Clinton campaign spokesman Brian Fallon.

“Director Comey owes the public an explanation for this inconsistency. If Director Comey is going to be forthcoming in matters related to Hillary Clinton, it is not fair for him to stay silent about investigations into election-related hacks,’’ said Fallon.

Trump has encouraged Russia to hack Democratic e-mail accounts, and his campaign has been dogged by business ties between a former campaign official, Paul Manafort, and figures in Ukraine who are friendly to Russia. NBC reported Monday that the FBI is conducting a “preliminary inquiry’’ into Manafort’s foreign business ties.

Mook called on Comey to explain why he was treating the Republican presidential nominee differently than Clinton, and to release information about any ongoing FBI investigations into ties between Trump, his campaign, or associates and Russian actors. The New York Times reported Monday night that the investigations have not found a link between Trump and the Russian government.

The CNBC story came on the heels of a scathing letter that Harry Reid, the Senate minority leader, sent to Comey on Sunday, in which the Nevada Democrat accused Comey of holding “explosive information about close ties and coordination between Donald Trump, his top advisors, and the Russian government.’’

Reid blasted Comey for ignoring previous requests to make the information public. “There is no danger to American interests from releasing it,’’ said Reid, who also accused Comey of a “clear double standard’’ for sending Congress his letter on the Clinton-related e-mails.

Uncertainty continues to swirl about the e-mails, which, according to news reports, were discovered on a computer owned by Anthony Weiner, a former Democratic congressman and the estranged husband of Clinton aide Huma Abedin. FBI agents discovered a cache of Abedin’s e-mails during an unrelated investigation into allegedly lewd texts Weiner sent an underage girl.

Comey said in July that a year-long probe into Clinton’s use of a private server and e-mail address while she was secretary of state did not turn up evidence of criminal activity, although he said the former secretary of state and her officials were careless in handling classified material. He said in his letter to Congress Friday that the new e-mails may be “pertinent’’ to that earlier review.

But according to news reports, it appears the FBI did not have a search warrant to look at Abedin’s e-mails, and thus no idea what they might contain, at the time Comey sent his letter to congressional leaders Friday alerting them, in cryptic prose, to the new development. The FBI has since gotten a warrant.

The White House Monday got into the act as well, with an oblique critique of Comey’s action so close to an election. Citing Justice Department guidelines that law enforcement should avoid major actions that could affect an election, spokesman Josh Earnest said, “The president believes that it’s important for those guidelines and norms to be followed.’’

But Earnest added that the president thinks Comey is a “man of integrity.’’

“He’s in a tough spot,’’ Mr. Earnest said.

The Real Clear Politics average of national polls says Clinton’s lead has shrunk to 3 points. The Clinton campaign has adopted a two-prong strategy to deflect possible damage wrought by the latest twist in the campaign. In addition to going on the attack against the director of the FBI, Clinton and her surrogates are expressing confidence that there is nothing to see in these new e-mails.

Campaigning in Ohio, Clinton urged voters, with the end of the campaign in sight, “Let’s not get distracted from the real choice in this election and the consequences for your future.’’

Victoria McGrane can be reached at victoria.mcgrane@globe.com.