Roger Stone Roger Jason StoneOur Constitution is under attack by Attorney General William Barr Justice IG investigating Stone sentencing: report Romney says Trump's protest tweets 'clearly intended to further inflame racial tensions' MORE, the longtime confidant of President Trump who was indicted Friday as part of special counsel Robert Mueller's Russia probe, appeared increasingly isolated on Sunday as current and former lawmakers warned that the charges against him are serious.

Rep. Adam Schiff Adam Bennett SchiffTop Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Overnight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Overnight Defense: House to vote on military justice bill spurred by Vanessa Guillén death | Biden courts veterans after Trump's military controversies MORE (D-Calif.), Sen. Marco Rubio Marco Antonio RubioFlorida senators pushing to keep Daylight Savings Time during pandemic Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Intelligence chief says Congress will get some in-person election security briefings MORE (R-Fla.) and former New Jersey Gov. Chris Christie (R) each sounded the alarm to varying degrees about the indictment of Stone, who is charged with one count of obstruction of an official proceeding, five counts of false statements and one count of witness tampering.

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For his part, Stone said on ABC's "This Week" that his attorneys view the charges as "thin as piss on a rock" and predicted that he would be acquitted in trial.

Schiff disagreed with that assessment of the indictment, calling the charges "very specific allegations of lies and witness intimidation."

"They’re matters that will be easily provable. These are not ambiguous statements. They’re very detailed. And I think he’s going to need a much better defense than the one you just heard," he said on "This Week" immediately following Stone's appearance on the program.

Rep. Adam Schiff responds to Roger Stone's denial of charges in the special counsel's indictment: "These are not ambiguous statements... I think he's going to need a much better defense than the one you just heard." https://t.co/BsxHgIP8si pic.twitter.com/WGmldiymT1 — This Week (@ThisWeekABC) January 27, 2019

Stone on Friday became the latest Trump associate to be charged or convicted in Mueller's investigation into Russian interference in the 2016 election.

Stone is a longtime ally of Trump, having served for decades as an informal adviser to Trump as Trump considering running for president on numerous occasions.

Stone joined Trump's 2016 presidential campaign shortly after Trump threw his hat in the ring in 2015, and the two remained in contact after Stone left the campaign in an official capacity in August 2015.

The indictment against Stone alleges that he communicated with WikiLeaks ahead of the 2016 presidential election and that he lied to Congress about those communications.

The indictment also states that a top Trump campaign official was instructed to contact Stone to get information about the WikiLeaks release of hacked Democratic emails ahead of the 2016 election.

It also alleges that around June and July of 2016, Stone told senior Trump campaign officials that he "had information indicating" that WikiLeaks had emails "whose release would be damaging" to Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE's campaign.

Stone, who in 2016 hinted on Twitter and in public that he had advance knowledge of the WikiLeaks email dumps, claimed on "This Week" that he never received "any stolen or hacked material." He said he he only took publicly available information and tried "to get it as much attention as possible."

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Rubio said on NBC's "Meet the Press" that "anyone who is cooperating" with WikiLeaks "is doing the work of a foreign intelligence agency to harm us."

"Suffice it to say it should be clear by now, and I think should have been clear to people a long time ago that WikiLeaks and others like that could have been tools of foreign intelligence used to divide America," Rubio said.

"And so I do believe that anyone who is cooperating with them, wittingly or unwittingly, is doing the work of a foreign intelligence agency to harm us," he added.

Rubio also said that working with WikiLeaks should be considered a crime "if you're wittingly doing it."

WATCH: Sen. @marcorubio talks Wikileaks on #MTP



"It should be clear by now ... that WikiLeaks and others like that could have been tools of foreign intelligence used to divide America.” pic.twitter.com/QDUWbiUNfd — Meet the Press (@MeetThePress) January 27, 2019

Christie, a Trump ally who served on the president's transition team, said during an interview on "This Week" that the "fact is that [Stone's] got a problem."

Christie, a former federal prosecutor, called the indictment "pretty damning" and predicted that Stone would be in "grave danger" if he decides to go to trial.

"They’ve got all these emails and text messages that he created that tell a pretty clear story, and I think it’s going to be very difficult for a jury to listen to that and conclude that it wasn’t what he was trying to do," Christie said.

“If he decides to go to trial, he’s in very, very grave danger," he added. "Everyone is presumed innocent, and so is he, but the indictment I think is a pretty damning indictment.”

On Roger Stone calling the special counsel's indictment "thin," Chris Christie says "it's not."



"The fact is that he's got a problem, because they've got all these e-mails and text messages that he created, that tell a pretty clear story." https://t.co/8is05mw7w6 pic.twitter.com/eTHnSgmg9G — This Week (@ThisWeekABC) January 27, 2019

Former associates of Stone also appear to be lining up to testify against him in court. Jerome Corsi and Randy Credico, who appeared before the grand jury that indicted Stone, have indicated that they would be willing to serve as witnesses if the case goes to trial.

Corsi, a conservative political commentator and conspiracy theorist, has been identified as "Person 1" in the indictment of Stone. He said Sunday on CNN's "State of the Union" that the information about him in the indictment is accurate and that he is willing to "affirm that" in court.

"I will affirm that what is in the indictment about me is accurate. And I will affirm that, if asked to in court," Corsi said.