(CNN) Congressional Republicans say the testimony of convicted former Trump campaign adviser George Papadopoulos raises questions about why the FBI decided to launch its counterintelligence investigation into Donald Trump's campaign and Russia.

Papadopoulos was interviewed Thursday behind closed doors for roughly seven hours. The two Republican lawmakers who attended the interview said that Papadopoulos has described his interactions with various officials in 2016, including Maltese professor Joseph Mifsud, who told him the Russians had dirt on Hillary Clinton.

"What we're finding is we have George Papadopoulos, the person who was supposedly the whole reason why we have this Russia collusion investigation going on, and yet he's never knowingly met with a Russian government official, he's never traveled to Russia," said Rep. Mark Meadows, a North Carolina Republican. "The facts that we're finding in here are astounding that we would allow this type of investigation to be embarked upon without any real solid foundation of collusion."

But Democrats argue that Papadopoulos' testimony is not credible, and his assertions are the product of a "right-wing echo chamber."

"He's been convicted of lying to the FBI, so you've got to take his testimony for what it's worth," said Maryland Rep. Jamie Raskin, the sole Democrat to attend Thursday's interview. "I see the whole thing as a footnote to a sideshow of a wild goose chase."

Papadopoulos played a central role in sparking the Russia counterintelligence investigation, which ultimately turned into the special counsel probe. The FBI launched the investigation in July 2016 after Australian diplomat Alexander Downer reported a conversation with Papadopoulos about the Clinton dirt, FBI officials have said.

The 31-year-old former campaign adviser was the first Trump official to plead guilty in special counsel Robert Mueller's probe , and he was sentenced last month to 14 days in prison for lying to the FBI about his interactions with Mifsud. Since Papadopoulos' sentencing, which he has not yet served, the former campaign adviser has become more vocal on Twitter and in the media, claiming his infamous meeting with Mifsud was in fact an attempt to set him up arranged by British and Australian intelligence officials.

"You couldn't expect a guy (me) who was linked into western diplomatic circles, and never knowingly met a Russian official, to all of a sudden be a patsy for a 'Russia' conspiracy," Papadopoulos tweeted this week. "My set up was carefully orchestrated."

Papadopoulos testified before the House Judiciary and Oversight Committees, where Republicans are investigating the FBI and the Justice Department's handling of the investigation into Trump's campaign and Russia.

Papadopoulos spoke briefly after interview concluded, saying his testimony had been transparent.

"I answered as truthfully as I possibly could," he said. "I can't get into details about what was discussed but I can just say I'm very happy with how it went and I'm looking forward to seeing any results that might come out of it."

He would not answer additional questions about what he specifically told lawmakers.

The Republican comments after the interview signal they're likely to point to his testimony to bolster their case that the Russia investigation never should have started. Meadows suggested Papadopoulos' Fourth Amendment rights could have been violated.

"It's hard to collude with someone if you don't know you're dealing with someone with the Russian government," said Rep. John Ratcliffe of Texas. "We continue to question why the FBI and the Department of Justice felt there was probable cause to be looking at figures like George Papadopoulos and Carter Page, who had either minimal or non-existent contacts with the Russian government."

Asked whether Papadopoulos provided any evidence to corroborate his claims that the British and Australians were involved with his interactions with Mifsud, Ratcliffe said Papadopoulos was explaining his own interactions.

"Mr. Papadopoulos has recounted the facts and the encounters that he has had with individuals. So from a personal knowledge standpoint, the things that lend themselves to his having those beliefs are what he's talked about," Ratcliffe said.

Ahead of his testimony, Papadopoulos' attorney for his congressional proceedings, Caroline Polisi, sent the committees a letter, obtained by CNN, stating he was prepared to speak about nine individuals, including Mifsud and Downer.

"He has nothing to hide, and in fact would like to better understand the circumstances leading up to his arrest," Polisi said in an email. "There will be no spin ... just facts. He has made mistakes in the past — for which he has openly accepted responsibility. He wants to move forward with his life and help the committees in any way that he can."

Papadopoulos' claims in recent weeks present a starkly different message than what was heard one month ago from Thomas Breen, who represented Papadopoulos for his criminal proceedings. Breen made no mention of any set up during Papadopoulos' sentencing, describing his client as naïve and stating that "the danger of dealing with Russia is not that obvious."

In addition to Papadopoulos, congressional Republicans have charged that the FBI and the Justice Department used information from the opposition research dossier on Trump and Russia — paid for by Democrats — to illicitly obtain a foreign surveillance on Page, another former Trump campaign adviser.

Democrats say that congressional Republicans are using their investigation as a way to undercut the Mueller probe and to protect Trump.

Still, they are likely to have their own questions about Papadopoulos' interactions with Mifsud — and whether he told anyone on the campaign about them.

Papadopoulos told CNN's Jake Tapper last month that he did not recall sharing the information from Mifsud with anyone on the Trump campaign, though he did not completely shut the door on the possibility.

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"As far as I remember, I absolutely did not share this information with anyone on the campaign," Papadopoulos said, adding, "I might have, but I have no recollection of doing so. I can't guarantee. All I can say is, my memory is telling me that I never shared it with anyone on the campaign."

While Papadopoulos hasn't testified before any of the congressional committees that investigated Trump and Russia over the past two years, his wife Simona Mangiante Papadopoulos spoke privately to House Intelligence Committee Democrats over the summer. Democrats on that committee have expressed an interest in speaking to Papadopoulos as well.