President Trump issued four tweets over 24 minutes Sunday, attacking special counsel Robert S. Mueller III’s probe as unfair and citing various Hillary Clinton controversies that he said warranted investigation. (Jabin Botsford)

Tensions between Republicans and Democrats over the investigation of Russian involvement in the 2016 presidential election intensified Sunday, with President Trump demanding to know why his campaign is under federal scrutiny while his former opponent Hillary Clinton is not.

The president's latest outburst over the inquiry led by special counsel Robert S. Mueller III surfaced on Twitter as his administration braced for the possibility that the first batch of charges in the case could be publicly announced as soon as Monday. CNN reported that a federal grand jury had approved an indictment, although details of the possible charges and the name of a defendant remained unclear.

Trump issued four tweets over 24 minutes, attacking the Mueller probe as unfair and citing various Clinton controversies that he said warranted investigation.

"Instead they look at phony Trump/Russia, 'collusion,' which doesn't exist," the president said. "The Dems are using this terrible (and bad for our country) Witch Hunt for evil politics, but the R's are now fighting back like never before. There is so much GUILT by Democrats/Clinton, and now the facts are pouring out. DO SOMETHING!"

Later in the morning, Trump added: "All of this 'Russia' talk right when the Republicans are making their big push for historic Tax Cuts & Reform. Is this coincidental? NOT!"

On Sunday talk shows, Republicans rallied around Trump and questioned how CNN could have received information about secret grand jury proceedings.

"There are very, very strict laws on grand jury secrecy, so depending on who leaked this to CNN, that's a criminal violation, potentially," New Jersey Gov. Chris Christie (R), a longtime friend of Trump's, said on CNN's "State of the Union" on Sunday. "For us to have confidence in this process, we've got to make sure that the grand jury process remains confidential, remains secret, so that the special counsel can work effectively to be able to get to the bottom of all that he's looking into."

House Majority Leader Kevin McCarthy (R-Calif.) cast doubt on the objectivity of Mueller's team, noting that the prosecutor's staff includes "a lot of individuals, attorneys who played in politics, who've given money on the Democratic side." Of the eight attorneys on the team who have been publicly identified, four made donations to Democrats, including President Barack Obama and Clinton.

"This president won the election solely on the idea that he connected with the American people. No other influence involved," McCarthy said on Fox's "Sunday Morning Futures." "But the idea of what I've watched, of what the Democrats have been doing, it sure raises a lot of questions."

Rep. Trey Gowdy (R-S.C.), chairman of the House Oversight Committee, came to Mueller's defense and said that he doesn't agree with Republicans who are calling for Mueller to resign or stop his investigation.

"I would encourage my Republican friends — give the guy a chance to do his job," Gowdy said on Fox News Sunday. "The result will be known by the facts, by what he uncovers . . . I would say give the guy a chance to do his job."

Democratic lawmakers mostly stayed out of the Sunday fray after a week in which Clinton's 2016 campaign came under fresh scrutiny. The campaign funded political opposition research into Trump that helped create a highly publicized "dossier" on the Republican candidate and fueled some allegations now under scrutiny by Mueller.

The 35-page dossier is composed of 17 memos containing raw intelligence, some of it highly salacious and not independently confirmed. It relies on Kremlin-linked sources and alleges that the Russian government had been trying to support Trump's candidacy while gathering compromising information that could be used as blackmail. The dossier was published in full by BuzzFeed in January.

It's unclear how much the Clinton campaign and Democratic National Committee paid for the opposition research by Fusion GPS, a Washington firm that conducts investigations for private clients. The Clinton campaign paid $5.6 million in legal fees to a law firm from June 2015 to December 2016, according to campaign finance records, and the DNC paid the firm $3.6 million in "legal and compliance consulting'' since November 2015. It's impossible to tell from the filings how much of that work was for other legal matters and how much of it related to Fusion GPS.

Trump tweeted Sunday morning that the dossier, which he called "Clinton made Fake Dossier," could have cost as much as $12 million, although he did not explain how he reached that number.

Trump was at it again early Monday. In a tweet, Trump again cited funding reports without elaborating on a source. "Report out that Obama Campaign paid $972,000 to Fusion GPS," Trump wrote. "The firm also got $12,400,000 (really?) from DNC. Nobody knows who OK'd!"

Compiled by former British intelligence agent Christopher Steele, the dossier mirrors a separate conclusion reached by U.S. intelligence agencies that the Russian government intervened in the U.S. election in an effort to bolster Trump and harm Clinton, such as through hacking the DNC and distributing materials to WikiLeaks to publish at key moments.

Fusion GPS, which hired Steele to gather information, was first employed to investigate Trump during the Republican primaries by the Washington Free Beacon, a conservative publication that receives financial support from billionaire GOP donor Paul Singer, according to two people familiar with Singer. The Beacon said in a statement that its research ended before Fusion GPS hired Steele and that none of the research that it commissioned is included in the dossier.

In April 2016, an attorney for Clinton's presidential campaign and the DNC hired Fusion GPS, which then hired Steele. Brian Fallon, a former spokesman for the Clinton campaign, said he learned about Steele and the dossier after the election. People familiar with the matter told The Washington Post that the Clinton campaign and the DNC did not direct Steele's activities.

Rep. Adam B. Schiff (Calif.), the ranking Democrat on the House Permanent Select Committee on Intelligence, said Sunday that "a lot" of the information in the dossier has been corroborated.

"I certainly would have liked to know who paid for it earlier, but nonetheless, that's just one factor to be considered," Schiff said on ABC's "This Week" on Sunday. "It doesn't answer the ultimate question, which is: How much of the work is accurate? How much of it is true? And my colleagues don't seem particularly interested in that question, but that is really the most important question for the American people."

Schiff said he has not been told anything about any impending indictments in Mueller's investigation, noting that such notification would not have been appropriate.

Trump also tweeted Sunday about Clinton's involvement in what he called the "Uranium to Russia deal," demanding that the matter receive greater scrutiny.

The 2010 deal approved by the Obama administration while Clinton was secretary of state allowed a Russian nuclear energy agency to acquire a controlling stake in a Canadian-based company that had mining licenses for about 20 percent of U.S. uranium extraction capacity. The company cannot export the uranium.

Earlier this month, House and Senate Republican leaders announced they would investigate the uranium deal, and the House Oversight Committee launched a probe into how the FBI investigated Clinton during the campaign. In the latter investigation, Republicans say they want to know why then-FBI Director James B. Comey publicly announced that the bureau was investigating Clinton but waited months before making a similar announcement about its inquiries into the Trump campaign.

Ed O'Keefe, Karoun Demirjian and Brian Murphy contributed to this report.